The San Jose mass killer had 12 guns and 22,000 rounds of ammunition inside his home, according to authorities.
Samuel Cassidy, 57, shot dead nine co-workers at a Valley Transportation Authority railyard in San Jose, California, before taking his own life.
"Based on current evidence obtained by Sheriff’s Office Detectives at the VTA yard and the suspect’s residence, it is clear that this was a planned event and the suspect was prepared to use his firearms to take as many lives as he possibly could had Sheriff’s Deputies not made entry to stop his rampage," the Santa Clara County Sheriff's Office said in a statement on Friday.
Sheriff Detective Sergeant Joseph Piazza said the weapons had been deliberately placed throughout the home.
“Based on my experience, I would think that weapons would be stored in different locations and placed there to access them in a time of emergency,” he said.
“If he was contacted by someone or law enforcement, he would have access to those weapons in various areas of the house.”
Santa Clara County Sheriff Laurie Smith has said Cassidy apparently shot himself as deputies closed in on him and that he was armed with three guns.
Authorities have not yet confirmed a motive for the killings, but have said that Cassidy appears to have been a disgruntled employee at the VTA.
San Jose officials also said that they were never told that Cassidy had been stopped by US Customs officers in 2016 and was found to have books on terrorism and a note book full of hateful writings about his workplace.
A Department of Homeland Security official has told CNN that Cassidy was stopped when returning to the US from a trip to the Philippines.
“Whatever this detention at the border was, it did not result in an arrest that showed up on his FBI criminal history, and it was not reported to SJPD," San Jose Mayor Sam Liccardo's office said in a statement.
