More information is coming out about the gunman who carried out a mass shooting in San Jose, California, only days after he killed eight co-workers at a Santa Clara Valley Transportation Authority (VTA). As in many cases of this nature, the shooter showed signs of violence and even made it onto the government’s radar before he went on his rampage.

The Wall Street Journal reported:

U.S. Customs officers had previously detained the man who killed nine people in San Jose, Calif., on Wednesday and found that he professed a hatred of his workplace where the shooting occurred, according to a Department of Homeland Security memo.

The gunman had “books about terrorism and fear and manifestos…as well as a black memo book filled with lots of notes about how he hates the VTA,” according to a CBP memo. This evidence was discovered after he was detained in 2016 while attempting to return to the U.S .after a trip to the Philippines.

The shooter worked at the VTA for about nine years and showed signs that he resented his place of employment and his co-workers despite telling the CBP agents that he said “no” when asked if he had issues with anyone at his work.

The memo was shared within the Department of Homeland Security (DHS) after the shooting. It did not indicate how long the shooter was held by border authorities. The Wall Street Journal could not confirm whether the memo was shared with the VTA or local law enforcement prior to the shooting.

So far, the motive for the shooting has not been determined. Laurie Smith, the Santa Clara County Sheriff, told reporters on Thursday that investigators have not yet found evidence pointing to why the shooter committed the crime.

Court records revealed that the gunman had a disturbing past.

From the Journal:

Cassidy’s ex-girlfriend said he sexually assaulted her, according to documents she filed in 2009 with the Santa Clara County Superior Court. She said Cassidy had bipolar disorder and “major mood swings” that were exacerbated when he consumed large amounts of alcohol.

She filed the court declaration in response to a domestic violence restraining order Cassidy had filed against her. She denied Cassidy’s accusations.

The suspect’s ex-wife, Cecilia Nelms, told the Associated Press that he often talked about murdering people about ten years ago. “She said he would return from work angry over assignments that he perceived to be unfair. The couple divorced in 2005 and Ms. Nelms said they hadn’t been in touch in 13 years,” according to the Journal.

The CBP memo did not explain why the agency detained the gunman but noted that he had a “minor criminal history.” It referred to a 1983 incident in which he was arrested and charged with “misdemeanor obstruction/resisting a peace officer.”

Sheriff Smith stated that the shooter was armed with two semiautomatic handguns with 11 magazines when he opened fire on his co-workers on Wednesday morning. On the morning of the shooting, a home belonging to the gunman was set on fire. Smith told the “Today Show” that he set an explosive device to detonate at his home at the same time he carried out the shooting.

The shooting occurred at a union meeting at the VTA rail yard in downtown San Jose. The victims were VTA employees. Police officers found eight people were dead at the scene. A ninth succumbed to their injuries overnight at the hospital. The shooter killed himself during the incident.