Does it really matter what caused him to snap? People snap all the time, we need to be able to defend ourselves from those who do.
Check it out:

The soldier who shot three people to death at Fort Hood apparently did not see combat during a tour in Iraq three years ago but was clearly troubled, under treatment for depression and anxiety and being evaluated for post-traumatic stress disorder.

As authorities tried to piece together a motive on Thursday for the rampage, a picture began to emerge of the gunman, identified as Spc. Ivan Lopez, 34, a married father who transferred from another base in Texas in February.

Lopez served eight years in the Army National Guard in Puerto Rico before enlisting in the Army in June 2008, military officials told the Senate on Thursday. He was assigned to Fort Bliss, Texas, before transferring to Fort Hood two months ago, according to military records.

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