SAN FRANCISCO, CA (KRON) – San Francisco Police investigators are providing new information more than a week after a mass shooting at a UPS facility. SFPD has interviewed more than 100 witnesses and recovered video from the UPS facility.

However, the shooting itself was not captured on camera.

Last week, Jimmy Lam fired 20 rounds from a semi-automatic pistol killing three fellow workers at the San Francisco warehouse before taking his own life.

At 8:50am last Wednesday, there was a daily meeting in the UPS facility that was attended by the gunman and the victims. Police say during that meeting Lam opened fire without warning, shooting four people in the meeting. Two of the victims died from their injuries.

Lam then walked outside the building and shot another victim multiple times. Lam then walked back into the UPS building. When officers arrived on scene, they confronted him and Lam took his own life.

Police say the three victims that died appeared to have been targeted.

Lam was armed with multiple guns, two of which were stolen, and one box of ammunition. The weapon used in the shooting, which is an assault type pistol, was stolen from a person in Utah. Lam also had a semi-automatic handgun stolen from Napa County, California.

Commander Greg McEachern said it was not known if Lam stole the weapons or if someone else did.

Investigators said Friday that they are not sure of a motive for the shooting. A San Francisco Police Department official has said Lam appears to have felt disrespected by co-workers, but the official did not know if that motivated the shooting.

The three drivers who were killed last Wednesday were known as kind and helpful among coworkers and clients, wounded driver Alvin Chen told The Associated Press in an interview. It would have been out of character for them to single anyone out for disrespect, he added.