The gunman who authorities say killed nine coworkers in San Jose, California, had a hatred for his workplace that he expressed in notes discovered when he was searched almost five years ago, a Department of Homeland Security official told CNN on Thursday.
Samuel James Cassidy was taken into secondary inspection after returning from a trip to the Philippines on August 8, 2016, and US Customs and Border Protection officers searched his belongings, the official said.
In addition to a black memo book filled with notes about hatred towards the Valley Transportation Authority, officers also found books about terrorism and fear and manifestos, the official said.
The Wall Street Journal first reported the CBP's search of Cassidy.
Cassidy, 57, died Wednesday morning of an apparent self-inflicted gunshot wound after taking three pistols to work at the light rail yard and shooting nine people, authorities said. A law enforcement official told CNN that the gunman appeared to target specific victims.
Authorities have yet to establish a motive for the shooting, but court documents and interviews with those who knew the gunman describe a man with anger issues dating back at least a decade.
Here is what we know about him:
He was a VTA employee
The shooting took place at about 6:30 a.m. PT at a light rail yard in San Jose as employees were starting trains up for the day, authorities said.
Law enforcement officers quickly arrived to the scene but did not exchange gunfire with Cassidy.
"I know for sure that when the suspect knew the law enforcement was there, he took his own life. Our deputies were right there at that time," said Santa Clara County Sheriff Laurie Smith.
"It's clear the victims and all the colleagues knew the shooter well," San Jose Mayor Sam Liccardo told CNN's Jake Tapper on Wednesday.
No apparent follow-up to 2016 detention, official says
Cassidy was detained by CBP officials in 2016, at least in part because of red flags regarding sex tourism in that part of the world, the DHS official said. There is no indication that anything related to sex tourism was found.
It doesn't appear that follow-up action was taken after the 2016 search, the official said.
After mass shooting incidents, CBP and other federal law enforcement agencies typically review their files to determine if they have had any prior interaction with suspects.
Cassidy traveled at least one more time to the Philippines after the 2016 inspection, the official said, but it's unclear if he was extensively searched after that subsequent trip.
CBP has broad authority to search travelers at airports and other places people enter the United States, like airports.
The Santa Clara Sheriff's Office said in a news release Thursday: "Based on recent developments in the investigation we can say that the suspect has been a highly disgruntled VTA employee for many years, which may have contributed to why he targeted VTA employees."
Suspect had three guns and 'precursor' to explosives
Cassidy had three 9mm pistols and 32 high-capacity magazines, the Santa Clara County Sheriff's Office said Thursday. The magazines, which hold more than 10 rounds, are illegal to possess in California.
Sheriff Smith earlier told CNN the gunman had two semi-automatic handguns and 11 magazines on him.
The three guns were legally obtained and registered, FBI San Francisco special agent in charge Craig Fair told CNN.
Fair said he believes the three handguns were used during the attack, noting at one point during the shooting spree one of the pistols jammed.
The gunman had 11 high-capacity magazines on his belt when officers located his body, Fair said.
The gunman fired 39 bullets in all and investigators preliminarily believe he appeared to target his victims, the sheriff told CNN. During his rampage, the shooter told a local union official who was present but did not work for the VTA, "I'm not going to shoot you," according to Smith.
Federal investigators have not found any manifesto or writings that would indicate a motive, Fair said, but noted local law enforcement was exploring the suspect's social media presence for clues.
Fire at house apparently owned by gunman
A house that erupted in flames Wednesday morning around the same time as the shooting is believed to be the gunman's home, a source close to the investigation told CNN.
City property records indicate Cassidy lived at 1178 Angmar Court. The San Jose Fire Department said firefighters responded at a home in the 1100 block of Angmar Court at 6:36 a.m. local time, just minutes after police were called about the VTA shooting about 8 miles away.
It took firefighters about an hour to extinguish the two-alarm fire, which caused heavy damage and left the structure uninhabitable, the fire department said.
During a sweep of the VTA crime scene, bomb-sniffing dogs alerted to the suspect's locker and found "precursor things for explosives," Smith said.
She said the precursor devices included detonation pulls.
The FBI's Fair said investigators recovered intact Molotov cocktails, made with paint thinners and alcohol, and multiple weapons at the gunman's home.
Surveillance video obtained by CNN shows a man identified as Cassidy leaving his home on Wednesday morning with a duffle bag. A neighbor, who did not want to be named, said the video was captured around 5:40 a.m. and showed Cassidy leaving the house in a truck. The neighbor described Cassidy as a "quiet" and "strange" man.
Fair said security camera footage analyzed by the law enforcement shows Cassidy arriving at the transportation facility around 5:30 a.m. local time, approximately one hour before the time the shooting reportedly started.
The women in his life said he had anger issues
Cassidy had a strained relationship with an ex-girlfriend, court documents show, which revealed troubling allegations she made in a filing in 2009 as she responded to a restraining order he filed against her.
The woman says she dated Cassidy for approximately one year in what she said became an off-and-on-again relationship after about six months.
She described Cassidy as having mood swings that were "exacerbated when (Cassidy) consumed large quantities of alcohol," she said in the court document, and she alleged he had bipolar disorder.
She said he enjoyed playing mind games with her, according to the court document.
"Several times during the relationship he became intoxicated, enraged and forced himself on me sexually," said the former girlfriend, who CNN is not naming and is reaching out to for comment.
Cassidy's ex-wife, Cecilia Nelms, told CNN affiliate the Bay Area News Group he resented his work. Nelms was married to Cassidy for about 10 years until the couple filed for divorce in 2005. She has not been in touch with her ex-husband for about 13 years, according to the outlet.
"He had two sides," Nelms said. "When he was in a good mood he was a great guy. When he was mad, he was mad."
He often spoke angrily about his coworkers and bosses, and at times directed his anger at her, Nelms told the outlet.
When the two were married, he "resented what he saw as unfair work assignments" and "would rant about his job when he got home," she said.
"He just thought that some people got more easy-going things at work, and he'd get the harder jobs," she said.