The Killer was depressed and upset that he had no girl friend.

http://www.nbcnews.com/storyline/oregon-college-shooting/oregon-shooting-umpqua-gunman-chris-harper-mercer-what-we-know-n437351

Authorities told reporters that the shooter had amassed 13 weapons — all purchased legally by either him or a family member from a federal gun dealer.

Six of the weapons were recovered at the scene and seven from his home, said Celinez Nunez, an assistant special agent in charge with the Bureau of Alcohol, Tobacco, Firearms and Explosives. The guns taken from the home were two pistols, four rifles and one shotgun, the Douglas County Sheriff's Office said.

In addition, investigators at the school recovered a flak jacket with steel plates lying next to a rifle and five magazines. Additional ammunition was found in the home, Nunez said.