The San Jose officers are still struggling to figure out the motive behind the mass shooting in the VTA rail yard on Wednesday, May 26. Officials confirmed with NBC News on Thursday that Samuel Cassidy, the shooter behind the mass shooting, fired at least 39 shots on the day of the tragic incident.

It can be remembered that the shooting incident in San Jose occurred during a busy morning in the rail yard as the overnight employees are handing out their duties to the next employee assigned on the early shift.

READ NEXT: California Police Officer Killed in Shootout; Suspect Committed Suicide

San Jose Rail Yard Shooting: Motive Still Unknown

Santa Clara County Sheriff Lauri Smith confirmed that their department still does not know what prompted the gunman to shoot his colleagues in the rail yard.

"What in the world could possibly prompt someone to take this kind of action," asked Sheriff Smith in an interview that also took place on Thursday. Sheriff Smith also told Associated Press that she is unsure if they will find the real motive, "but we'll piece it together as much as we can from witnesses."

Cassidy was reported to arrive in the area of the incident on Wednesday at around 6:00 a.m., with a duffel bag filled with semi-automatic handguns and a high-capacity magazine. Sheriff Smith added that Cassidy had at least 11 loaded magazines with him during the shooting incident.

Moreover, officers believe there was more ammunition inside Cassidy's home, which went into a fire the same moment as the shooting erupted in the San Jose rail yard. This is because firefighters smelled an accelerant when they arrived at Cassidy's residence.

Meanwhile, Sheriff Smith also verified that the dead bodies of the victims were found in two buildings. Although there were no cameras inside the building, the sheriff mentioned footage that captured him moving from one location to the next.

"He knew where employees would be," said Smith, adding that they responded at the scene within a few minutes.

San Jose Shooter Hates Work

Associated Press highlighted a Biden official disclosing that Cassidy spoke of hating his workplace when customs officers detained him after a 2016 trip to the Philippines. After being detained, the unnamed Biden official said the shooter was found with a memo with notes of his anguish about VTA. It was also learned from the memo that Cassidy had an arrest in San Jose in 1983 with charges of misdemeanor obstruction/resisting a peace officer.

Furthermore, Cassidy's former wife said that more than a decade ago, the shooter at some point talked about killing people at work. The ex-wife furthered that Cassidy would come home resentful and angry over "unfair" assignments.

San Jose Mass Shooting Death Toll, Now at 10

The nine employees killed in the San Jose rail yard mass shooting were Abdolvahab Alaghmandan, Adrian Ballezza, Alex Ward Fritch, Jose Dejesus Hernandez III, Lars Kepler Lane, Paul Delacruz Megia, Timothy Michael Romo, Michael Joseph Rudometkin, and Taptejdeep Singh. 

Initial reports mention nine casualties, including the suspect, Cassidy. However, Alex Ward Fritch died in the hospital hours after, bringing the total deaths in this mass shooting to 10.

READ MORE: Colorado Springs Shooting: 7 Dead Including Suspect When Birthday Party Turns to Massacre

WATCH: Sheriff: gunman in Calif. appeared to target victims - from Associated Press