An autopsy has determined that Samuel James Cassidy, the gunman who killed nine co-workers May 26 at a Santa Clara Valley Transportation Authority maintenance yard, died of suicide from multiple gunshot wounds to the head.

The Santa Clara County Office of the Medical Examiner-Coroner said in a press release, “Although rare, this can occur in suicides in which the first shot to the head was not immediately fatal.”

“The Medical Examiner-Coroner's Office is providing the cause and manner of death findings following a thorough crime scene investigation and autopsy,” according to the press release.

Earlier Tuesday, body-worn camera footage released by the Santa Clara County Sheriff's Office showed the tense moments as deputies and San Jose police officers entered a building at a VTA maintenance yard in a search for the gunman who killed nine co-workers and then himself.

This video contains graphic images.

In the video a deputy, a sheriff's supervisor and three San Jose police officers enter the building with a key card borrowed from a VTA supervisor.

Gunshots can be heard near the end of the four-minute video after officers make their way to the third floor, through darkened offices and down a hallway during the search for 57-year-old Samuel Cassidy, who has been described by investigators as a “highly disgruntled VTA employee for many years.”

They then enter a room where Cassidy, his face blurred out, can be seen slumped on a desk chair by a stairwell. Broken glass from a window by the door to a transportation superintendent's office is visible to the left.

Santa Clara County Sheriff Laurie Smith at a news conference Tuesday praised the collaboration between deputies and police officers and their training and protocols in active shooter situations, noting there were still some 100 workers and that Cassidy “had a lot of additional ammunition” at the yard at the time.

“I thought it was important to show this protocol saved lives,” she said.

Every law and fire agency in the county has been trained in a recently created active shooter protocol in which two to five officers form a rescue task force able to work together between departments before entering what is known as a “warm zone,” sheriff's spokesman Deputy Russell Davis said.

“I hate to say it, but if we did not have the protocol and they did not make contact, this would have been a lot worse,” Davis said.

He said 11 gun magazines with full ammunition capacity were found on the grounds of the maintenance yard, in addition to thousands of rounds found at Cassidy's home.

Smith said a specific motive for the shooting is still being investigated. She said authorities do not know if Cassidy had made any threats beforehand.