Investigators have been at the suspect's home on Angmar Court since Wednesday searching every corner of the house. They found Molotov cocktails inside Friday morning. Multiple sources told ABC News the Molotov cocktails were completed, but did not explode. Authorities aren't sure why he had the volatile concoctions, but it could have been an attempt to accelerate the fire at his home.
PHOTOS: Molotov cocktails, weapons found at VTA attack suspect's home
The suspect, 57-year-old VTA employee Sam Cassidy, set fire to his home on Angmar Court before going to the light rail yard and control center where he shot and killed nine people.
Deputies say Cassidy set the fire by putting ammunition inside a pot on the stove, then placing additional accelerants around the stove. The ammunition heating on the stove eventually set the fire.
A locker at the rail yard believed to be the shooter's also contained "materials for bombs, detonator cords, the precursors to an explosive," said Santa Clara County Sheriff Laurie Smith.
"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 department said Friday.
Another suspicious device found at his home Friday turned out to be batteries and wires, San Jose officials said.
VIDEO: Suspicious device detonated at VTA shooting suspect's home
Suspicious device detonated at VTA shooting suspect's home
The house on Angmar Court was boarded up and cleared Friday afternoon, allowing neighbors to return to their homes.
Hundreds of people showed up outside San Jose City Hall Thursday night to remember the nine victims of Wednesday's mass shooting.
RELATED: Families share touching memories of VTA shooting victims during San Jose City Hall vigil
"My nephew and my niece, they're not gonna have a father. They're 3 and 1," said Tagtejdeep Singh's younger brother, Carmen. "They're going to ask where their father is. Nobody can bring them back, nor can I, nor can anyone else."
"My dad was the smartest and funniest man I know," said Timothy Romo's daughter, Audrey.
RELATED: These are the 9 victims of the VTA attack
"He was my hero and my idol, everything I ever wanted to be as a man and he led by example in everything he did," said Romo's son, Scott.
On Thursday, the Santa Clara County Sheriff's Office released new surveillance video showing the suspect during his shooting rampage. The video shows him walking away from one building where he shot multiple coworkers and towards another area where he would kill more victims, according to authorities.
New video shows VTA gunman during mass shooting
Law enforcement agencies announced the suspect had a long history of dissatisfaction with his employer.
He was once stopped by Customs and Border Protection while returning from the Philippines in 2016, sources tell ABC News. He was stopped and searched because he was carrying books about terrorism and manifestos, according to three sources familiar with the investigation. CBP found he was also carrying a notebook that detailed hatred of his workplace, the Valley Transportation Authority.
Santa Clara County District Attorney Jeff Rosen confirmed Friday that CBP and Homeland Security did not contact the county or the VTA at the time. Rosen added no complaints ever came into law enforcement about his weapons stockpile or his temper.
The man appears to have targeted some of his victims, according to the Santa Clara Sheriff's Department.
"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," the sheriff's department said in a statement.
EXCLUSIVE: San Jose shooting widow remembers 'soulmate' of 22 years
EXCLUSIVE: SJ shooting widow remembers 'soulmate' of 22 years
A witness who survived the shooting told ABC7 News that from his vantage point, it looked like the gunman didn't fire indiscriminately. Rather, he let some people live and chose to kill others.
The shooter had talked about killing people at work more than a decade ago, his ex-wife said.
"I never believed him, and it never happened. Until now," a tearful Cecilia Nelms told The Associated Press.
Editor's note: The Santa Clara County Sheriff's Department originally reported 22,000 rounds of ammunition were found at the suspect's home. They later said the number was actually 25,000 and this story has been updated to reflect that change.
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ABC7 News staff and the Associated Press contributed to this report.