Why did Tate murder the students?
Status Specifics
The house exerts demonic influence on men

Hugo raped Moira. Larry murdered Hayden, and Ben just covered it up by building a gazebo. Larry killed Beau, acting on Constance's instruction. Tate shot 15 people. NOTE: After Larry killed Hayden, Ben did have an emotional reaction to her death, so this theory may not hold up.

Tate's family is severely dysfunctional

This theory is, of course, not mutually exclusive with Theory #1. Which could lead him to his drug use.In the 10th episode, "Smoldering Children", there is a flashback of the Langdon family and Larry all having dinner. Constance yells at Tate for saying she doesn't love Larry. Their argument ends with Tate saying "No matter how much you want it I will never be your perfect son". Next it shows him turning off his alarm already awake. He is then seen snorting a white powder (Cocaine) and then grabbing guns from under his bed. He then sets off to set Larry on fire and shoot up his high school. It is well established that cocaine, especially in large doses over a short period of time, can make the user very violent.

Addie was bullied

Addy was bullied and/or molested; Tate was seeking revenge. Addy was in her 40s when she died. When Tate was a teen, Addy would have been already out of high school. And knowing Constance, she probably didn't even send Addy to school. It is still possible for students to have bullied her outside of the school.

Theory disproven
There was more than one killer
  • In the articles Violet was looking at online about the murders, they mention two killers. Maybe the second killer made Tate participate or made him want to kill. The picture with the articles referring to the two shooters is posted on the Westfield High/Massacre wikia page.
    (NOTE: Taken from the "Trivia" section of the Westfield High Massacre wikia page, which could possibly disprove this theory. "The search results are based on actual search results on Columbine, which is why they cite the "Trenchcoat Mafia," referring to the suicides by the perpetrators, although Tate did not kill himself, and to "suburban Los Angeles" and "unincorporated". Columbine is both unincorporated and suburban. Another possibility is therefore that the mentioning of "killers" and "criminals" is merely another reference to Columbine. The first article visible is based on the Wikipedia article on the Columbine High School massacre: 'occurred on Tuesday, April 20, 1999, at Columbine High School in Columbine, an unincorporated area of Jefferson County, Colorado'. The second search result visible refers to a USA Today article to commemorate the 10th anniversary of the Columbine massacre, "They weren't goths or loners". The line of the third article, "wasn't about jocks, goths or Trenchcoat Mafia" is taken from NY Times writer Dave Cullen's book 'Columbine' ".)

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