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7 November 2007 - Jokela school shooting.
7 November 2012 - 2012 Moscow shooting (Dmitry Vinogradov)

14 February 2008: Steven Kazmierczak kills five and commits suicide at Northern Illinois University
14 February 2018: Nikolas Cruz kills 17 and injures 17 at Stoneman Douglas High School in Florida

16 February 1988: Richard Farley kills seven and injures four at ESL Inc. in California
16 February 2009: Travis the chimp viciously attacks his owner's friend and is shot by police in Stamford, Connecticut
(Obviously, Travis isn't a mass shooter but this was important to Adam Lanza)

11 March 2008: Richard Novia, Adam Lanza's Tech Club advisor, is put on administrative leave from Newtown High School after an altercation with a student and Adam [You must be registered and logged in to see this link.] a series of reviews for computer parts on Newegg.com
11 March 2009: Tim Kretschmer kills 15 and commits suicide in Winnenden Germany

9 April 1953: Stephen Paddock is born
9 April 1981: Eric Harris is born
9 April 2011: Tristan van der Vlis kills six and commits suicide at a mall in the Netherlands

10 April 1998: Eric Harris starts his journal
10 April 2011: Anders Breivik signs the lease on the farm where he builds his bomb (which kills eight people)

16 April 2007: Seung-Hui kills 32 and commits suicide at Virginia Tech
16 April 2012: Criminal trial of Anders Breivik begins
16 April 2017: Cascade Mall shooter Arcan Cetin commits suicide by hanging in his cell at Snohomish County Jail

18 May 1960: Michael Ryan is born
18 May 2018: Dimitrios Pagourtzis kills 10 at Santa Fe High School in Texas

11 September 1981: Dylan Klebold is born
11 September 2014: Chardon High School shooter TJ Lane escapes from prison (and is caught the next day)

13 December 1987: James Holmes is born
13 December 2013: Karl Pierson kills one and commits suicide at Arapahoe High School in Colorado

14 December 1992: Wayne Lo kills 2 people and injures 4 at his college
14 December 1996: Steven Kazmierczak attempts suicide for the first time
14 December 2005: Seung-Hui Cho is court ordered to obtain outpatient mental health treatment
14 December 2012: Adam Lanza's murder spree and suicide

(Edit: I clearly misunderstood the topic of the thread. But I'll leave it.)

(Edit 2: I am going to keep adding to this list because why not.)

5 November 2009: Nidal Hasan kills 14 people (including 1 unborn child) at Fort Hood in Texas.
5 November 2017: Devin Kelley kills 26 (including 1 unborn child) at the First Baptist Church in Texas and kills himself after a car chase.

27th February 1930: English serial killer John Straffen was born

27th February 2012: Tj Lane kills 3 people at Chardon High School

October 1
Stephen Paddock (Las Vegas strip)
Chris Harper Mercer (Umpqua College)
Luke Woodham (Pearl High)

September 23
Arcan Cetin (Cascade Mall)
Matti Saari (Kauhajoki College - exact name of institution escapes me)
Éric Borel (Cuers, France)

Russianman wrote:

7 November 2007 - Jokela school shooting.
7 November 2012 - 2012 Moscow shooting (Dmitry Vinogradov)

Ian David Long (Borderline Bar and Grill) same date

15 March 2016: Anders Breivik in court

15 March 2019: Brenton Tarrant kills 51 people in Christchurch New Zealand

May 7, 1967: Martin Bryant is born.
May 7, 2019: Colorado STEM school shooting.

May 20th 1998 Kipland Kinkel kills his parents
May 20th 2016 David Ali Sonboly buys the Glock 17 he would kill 9 people with before commiting suicide 2 months later.

June 4th 1989 Pekka Eric Auvinen is born
June 4th 2014 Moncton shooting

April 20th 1900: John Filip Nordlund is released from prison

April 20th 1999: Columbine High School Massacre

July 22, 2011 - Anders Breivik commits his attack in Norway.
July 22, 2016 - David Ali Sonboly commits his shooting at a Munich McDonalds and shopping mall.

April 9th, 1953 - Stephen Paddock is born.
April 9th, 1981 - Eric Harris is born.
April 9th, 2014 - Alex Hribal stabs 20 students and a security guard at Franklin Regional High School.

June 8th, 2001 - Mamoru Takuma kills 8 Japanese school children with a knife in Japan.
June 8th, 2008 - Tomohiro Katō kills 7 people with a truck and knife in Akihabara.

This isn't exactly what you're post is referring to but, 2007 both had shooters born in 1988.

August 4th 2009: George Sodini kills 3 women and injured 9 at LA fitness health club.

August 4th 2019: Connor Betts kills 9 people and injures 17 at Ned Peppers bar.

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april twentieth 07, johnson space center shooting in houston, resulting in death of two people including the perpetrator

2015 paris attacks 11/13 coincided with the twentyfifth anniversary of the aramoana massacre

9/1 myojo 56 building fire 01, beslan school siege 04

7/22/18 toronto shooting, perpetrated by mentally ill/psychotic gunman faisal hussain

cascade mall shooter arcan cetin hanged himself in prison on 4/16/17, tenth anniversary of virginia tech

On September 11, 2011, ten years after 9/11, future Boston Marathon bomber Tamerlan Tsarnaev and his friend murdered 3 drug dealers in their apartment.

November 7th, 2007 - Jokela school shooting.
November 7th, 2019 - Orlando Tavares State School attack.

April 16, 1980 - Yevgeny Manyurov is born.
April 16, 2007 - Virginia Tech shooting.

November 7, 2007 - Jokela High School shooting.

November 7, 2018 - Thousand Oaks Borderline Bar and Grill shooting.

December 13, 2012 - Adam Lanza’s mother, Nancy, comes home from her trip to New Hampshire (1 day before Sandy Hook shooting).

December 13, 2013 - Karl Pierson shoots and kills Claire Davis at Arapahoe High School them kills himself.

april 20th 1997 - dylann roof is baptised
april 20th 1999 - columbine shooting
september 11th 1981 - dylan klebold is born
september 11th 2001 - 9/11 happens

January 2nd 2001: Federico Guevara is born
January 2nd 1938: Ian Brady is born

17 January 1989: Stockton Cleveland Elementary School shooting
17 January 2000: Liu Shuangrui, the 2015 Hubei shooter, leaves Baoding psychiatric hospital, while there he was diagnosed with bipolar disorder.
17 January 2002: Bat Mitzvah massacre

November 14, 2019: Nathaniel Berhow kills 2 students and wounds 3 others before shooting himself

Also on November 14th, 2019: A 9 year old boy shoots and injures 3 of his classmates with a BB gun

Carnifex879 wrote:

November 14, 2019: Nathaniel Berhow kills 2 students and wounds 3 others before shooting himself

Also on November 4th, 2019: A 9 year old boy shoots and injures 3 of his classmates with a BB gun

Also: Amur College shooting (Daniil Zasorin).

March 13th, 2019 - Professor Raul Brasil State School shooting.
March 13th, 1996 - Dunblane massacre.

26 July 1989 Chris Harper-Mencer is born
26 July 1991 Tim Kretschmer is born

December 14th 2012 : Adam Lanza commits the Sandy Hook shooting
December 14th 2012 : Min Yongjun commits the Chengpeng Village Primary School Stabbing

September 13, 2006: Dawson College shooting (1 dead, excluding shooter, 19 injured)

September 13, 2017: Freeman High School shooting (1 dead, 3 injured)

September 11th, 2001 - September 11 attacks.
September 11th, 2001 - Ilnaz Galyaviev is born.

Some of these might stretch the definition of what you're looking for, but I hope it's interesting nevertheless.
August 30, 2006 - Kip Kinkel's 24th birthday
August 30, 2006 - Alvaro Castillo's attack on Orange High School (he was aware of Kips birthday and told police.)

June 1, 2004 - Michael Carneal turns 21
June 1, 2004 - Sasebo slashing, better known as the Nevada-tan murder.

November 14, 2017 - Rancho Tehama Reserve shootings
November 14, 2017 - Nathaniel Berhow turns 14. In less than a month, his father would die of a sudden heart attack

November 14, 2019 - Nathaniel Berhow commits the Saugus High School shooting before turning the gun on himself.
November 14, 2019 - 19-year-old Daniil Zasorin opens fire at school in Blagoveshchensk, Russia, killing 1, injuring 3, and killing himself after a shootout with police.
November 14, 2019 - Not really a shooting, but interesting nevertheless: a 9-year-old boy shot three students ages 9 to 12 with a BB gun at the playground of Washington Elementary STEM Magnet School, injuring them

May 25, 2018 - Santa Fe High School shooting
May 25, 2018 - "A 14-year-old male opened fire with a rifle at roughly 7:00 a.m. at Highland High School campus and walked into a bathroom, and wounded one former schoolmate, a male who was shot in his arm."

January 18, 1993 - Seung Hui Cho turns 9.
January 18, 1993 - East Carter High School Shooting

Another note about September 11:
September 11th, 2016 - Carter Boyles, also known as Bob8466, seems to have planned a shooting at Jefferson High School but instead committed suicide.
EDIT: this is wrong, I am stupid for trusting Encyclopedia Dramatica about anything.

On another note, I'm making a list of when attacks took place during the year in an attempt to spot and explain any spikes. I'll post any coincidences I discover in this thread.

April 28th, 2010 - Zheng Minsheng, perpetrator of the Nanping school massacre, is executed.
April 28th, 2010 - Chen Kangbing attacks Hongfu Primary School with a knife, wounding 17.

dyonqqr wrote:

Some of these might stretch the definition of what you're looking for, but I hope it's interesting nevertheless.
August 30, 2006 - Kip Kinkel's 24th birthday
August 30, 2006 - Alvaro Castillo's attack on Orange High School (he was aware of Kips birthday and told police.)

June 1, 2004 - Michael Carneal turns 21
June 1, 2004 - Sasebo slashing, better known as the Nevada-tan murder.

November 14, 2017 - Rancho Tehama Reserve shootings
November 14, 2017 - Nathaniel Berhow turns 14. In less than a month, his father would die of a sudden heart attack

November 14, 2019 - Nathaniel Berhow commits the Saugus High School shooting before turning the gun on himself.
November 14, 2019 - 19-year-old Daniil Zasorin opens fire at school in Blagoveshchensk, Russia, killing 1, injuring 3, and killing himself after a shootout with police.
November 14, 2019 - Not really a shooting, but interesting nevertheless: a 9-year-old boy shot three students ages 9 to 12 with a BB gun at the playground of Washington Elementary STEM Magnet School, injuring them

May 25, 2018 - Santa Fe High School shooting
May 25, 2018 - "A 14-year-old male opened fire with a rifle at roughly 7:00 a.m. at Highland High School campus and walked into a bathroom, and wounded one former schoolmate, a male who was shot in his arm."

January 18, 1993 - Seung Hui Cho turns 9.
January 18, 1993 - East Carter High School Shooting

Another note about September 11:
September 11th, 2016 - Carter Boyles, also known as Bob8466, seems to have planned a shooting at Jefferson High School but instead committed suicide.

On another note, I'm making a list of when attacks took place during the year in an attempt to spot and explain any spikes. I'll post any coincidences I discover in this thread.

Carter shot himself on Sept. 9, not Sept. 11.

November 24, 2008 - Adam Lanza’s parents file for divorce.
November 24, 2008 - "A 16-year-old shot and killed a 13-year-old classmate in Cabaret, Haiti, before fleeing the scene."

August 24, 2009 - Lanza registers for the course A+ Computer Repair at Norwalk Community College.
August 24, 2009 - Two pipe bombs went off in a hallway of Hillsdale High School. Alex Youshock, a 17-year-old former student of the school was found with eight other pipe bombs, a two-foot-long sword, and a chainsaw concealed in a guitar case.

March 16, 1993: Luiz Henrique de Castro Born.
March 16, 2021: Atlanta spa shottings

I know this isn't quite what you were looking for when you posted this, but there's also:
December 13, 2012: Adam Lanza drives by SHES, apparently as a form of reconnaissance.
December 13, 2013: Karl Pierson's attack at Arapahoe High School. December 14th, 2013 fell on a Saturday, so he had to do it early.

More correlations with important dates can be found [here.]

margaflor wrote:

March 16, 1993: Luiz Henrique  de Castro Born.
March 16, 2021: Atlanta spa shottings

Two more,
March 16, 2000: Brannenburg, Germany school shooting
March 16, 2017: Grasse, France school shooting

Sandy Hook Elementary school shooting happened on the December the 14th. December the 14th is also a "Monkey Day" -https://en.wikipedia.org/wiki/Monkey_Day
It may be a simple coincidence or a deliberate choice since Adam was obsessed with a chimp society and other stuff related to apes.

september 28, 2004: carmen de patagones shotting
september 28, 2017: Stephen Paddock checks into the 32nd floor of the Mandalay Bay Resort

April 20, 1999 - Columbine High School massacre.
April 20, 2000 - 15 year old goes on stabbing spree at Cairine Wilson Secondary School, injuring five.
April 20, 2015 - Barcelona school killing, where a 13-year-old boy, armed with a homemade crossbow, a machete, and Molotov cocktails, killed 2 and injured 4.
(Alex Hribal wanted to commit his stabbing on April 20th, 2014, but it was a Sunday.)
(Alvaro Castillo wanted to kill himself on April 20th, 2006, but didn't.)

January 29, 1979 - Brenda Ann Spencer opens fire at Cleveland Elementary School
January 29, 2008 - Madhu school bus bombing
January 29, 2013 - 2013 Alabama bunker hostage crisis

Some of the following are blatantly stolen from elsewhere in the thread, so it's more of a compilation I can't take full credit for:
September 11, 1909 - A teacher at Bear Hollow School shoots a student who drew a knife on him
September 11, 1975 - Grant High School shooting by James Briggs.
September 11, 1981 - Dylan Klebold is born
September 11, 1992 - Six students were shot at Palo Duro High School, all survived the shooting.
September 11, 2001 - 9/11 attacks.
September 11, 2001 - Ilnaz Galyaviev is born.
September 11, 2004 - Man attacks 28 children at a kindergarten in China with with a knife and explosives
September 11, 2011 - Future Boston Marathon bomber Tamerlan Tsarnaev and his friend murdered 3 drug dealers in their apartment.
September 11, 2014: Chardon High School shooter TJ Lane escapes from prison (and is caught the next day)
Whole day's cursed.

March 6, 2009 - A 15-year-old male is shot in the foot during a fashion show at Westover High School by Terrance Donnell Johnson, Jr.
March 6, 2009 - Scott Beierle purchased a .40 caliber Glock handgun from Uncle Sam’s Pawn and Gun located in Lawton, Oklahoma.

August 29, 2011 - A 30-year-old woman slashed eight children with a box cutter at a child-care centre in Shanghai, wounding one seriously. T
August 29, 2011 - Scott Beierle enrolled at Florida State University.

23 April 1992: Lu Benbiao kills 4 and injures 93 at Jintoucun village with explosives.
23 April 1992: Adam Lanza turns one day old (or maybe he was born that day, depending on how you interpret the timezones.)

30 December 2009: Adam Lanza registers the username Smiggles on Shocked Beyond Belief.
30 December 2009: A drunken Huang Yangfang kills 7 and wounds 13 with a knife and a hoe in Changshan village.

29 August 2011: Nancy Lanza orders one Blackhawk Universal Tactical Sling and a custom gas plug for the Saiga shotgun.
29 August 2011: An unnamed woman working at a Minhang daycare wounds eight children with a boxcutter.

4 December 2012: Nancy Lanza plans an upcoming trip to London, which had to be rescheduled.
4 December 2012: Liu Shuangyun kills 14 and injured 2 with an arson attack in Shantou.

20 March 2005: Jeff Weise makes final preparations on the day before his attack at Red Lake High School.
20 March 2005: He Xiangyue kills 9 and injures an unclear number of people at Yibin and is arrested and executed.

September 19, 1994: Thomas Michael "T.J." Lane III is born
September 19, 1994: Soweto school shooting, 7 wounded

April 14, 2003 - John McDonogh High School shooting.
April 14, 2003 - Maya Elizabeth McKinney (Alec McKinney) is born.

margaflor wrote:

March 16, 1993: Luiz Henrique  de Castro Born.
March 16, 2021: Atlanta spa shottings

Not a rampage in the traditional sense, but this is also the same date in 1968 as when the infamous My Lai massacre occured, in which US Army soldiers killed, raped, and toryured hundreds of Vietnamese villagers during the Vietnam War.

dyonqqr wrote:

I know this isn't quite what you were looking for when you posted this, but there's also:
December 13, 2012: Adam Lanza drives by SHES, apparently as a form of reconnaissance.
December 13, 2013: Karl Pierson's attack at Arapahoe High School. December 14th, 2013 fell on a Saturday, so he had to do it early.

Also not a rampage attack, but December 13th 1937 is the day the Rape of Nanking was carried out by the Imperial Japanese Army during WWII, leading to as many as 300,000 deaths, nearly as many rapes, and much of the city reduced to a smoldering ruin from six continuous weeks of violence.

dyonqqr wrote:

Some of the following are blatantly stolen from elsewhere in the thread, so it's more of a compilation I can't take full credit for:
September 11, 1909 - A teacher at Bear Hollow School shoots a student who drew a knife on him
September 11, 1975 - Grant High School shooting by James Briggs.
September 11, 1981 - Dylan Klebold is born
September 11, 1992 - Six students were shot at Palo Duro High School, all survived the shooting.
September 11, 2001 - 9/11 attacks.
September 11, 2001 - Ilnaz Galyaviev is born.
September 11, 2004 - Man attacks 28 children at a kindergarten in China with with a knife and explosives
September 11, 2011 - Future Boston Marathon bomber Tamerlan Tsarnaev and his friend murdered 3 drug dealers in their apartment.
September 11, 2014: Chardon High School shooter TJ Lane escapes from prison (and is caught the next day)

Rounding this list out (and the third non-rampage I have to mention thus far), September 11th, 1973 was the day Augusto Pinochet took over the country of Chile in a coup and proceeded to restructure the country into a far right dictatorship where thousands were killed at home and abroad and over 100,000 were detained and tortured in manners more befitting of the Medieval era rather than the 20th century.

dyonqqr wrote:

April 28th, 2010 - Zheng Minsheng, perpetrator of the Nanping school massacre, is executed.
April 28th, 2010 - Chen Kangbing attacks Hongfu Primary School with a knife, wounding 17.

April 28th, 1999 - W R Myers High School Shooting
April 28th-29th, 1996 - Port Arthur Massacre