That is an easy answer, they were crazy and it had nothing to do with terrorism.
Terrorism Noun:Both shootings were committed by young men with mental health problems and had no political motive. While both shootings did scare people, they do not fit the definition of terrorism. Hence that is why it doesn't need to be investigated by congress. Now, if they choose to do a hearing on mental health in this country then both these shootings would of course be included. But, since this hearing is specifically on the growth of terrorism being committed by Americans they don't belong in these hearings.
the use of violence and threats to intimidate or coerce, especially for political purposes.
- September 19: Najibullah Zazi, an Afghan citizen and U.S. legal resident, is arrested on charges of conspiracy to use weapons of mass destruction. Authorities claim that Zazi traveled to Pakistan to receive explosives and weapons training and that he planned to launch an attack in the U.S.
- November 5: Army Major Nidal Malik Hasan allegedly kills 13 and wounds 30 at Fort Hood Army Base, outside Killeen, Texas. Early reports reveal that Hasan had been in contact with radical Yemeni cleric Anwar al-Awlaki.
- November 23: Federal officials unseal indictments against eight people charged in connection with the alleged recruitment of up to two-dozen Somali-Americans to fight with the Somali insurgent group and al Qaeda affiliate, al-Shabaab.
- December 8: The F.B.I. accuses U.S. citizen David Coleman Headley of conspiring with operatives of Lashkar-e-Taiba, a Pakistani terrorist group, in the 2008 Mumbai attacks. Authorities also allege that Headley had planned to attack a Danish newspaper.
- December 9: Five young Northern Virginia men are arrested in Sargodha, Pakistan. U.S. and Pakistani authorities claim the group traveled there to fight alongside Taliban militants in Afghanistan
There are some realities that have to be faced. The vast majority of terrorism around the world is done in the Islam. Many terrorism experts say that about 7% of Muslims have been radicalized. While that seems like a very small percentage, there are more than a billion Muslims worldwide. That gives a very high number of radicals running around plotting to kill non believers and infidels.