A survivor of the shooting at a San Francisco UPS warehouse says he was standing in his usual spot during a weekly meeting when he heard a loud pop like a firecracker behind him.

When Alvin Chen heard a second pop, he felt pain, looked down and saw blood pouring down his leg.

Chen, 43, cried at times as he told The Associated Press on Monday about the chaotic shooting inside a UPS warehouse last week. Jimmy Lam, 38, killed three fellow drivers and wounded two others before he killed himself in front of police.

Chen said he got into the cab of the truck closest to him, hoping to hobble out through the truck’s rear door and slip down a hallway and into the street.

He was about 60 feet (18 meters) from the exit when he saw Lam blocking his path, scanning the room as if looking for someone.

“But I don’t know who he’s looking for,” Chen said.

He turned back, checking to make sure he wasn’t being followed. He encountered another UPS driver hiding behind a truck before he noticed a body on the ground. It was his friend Wayne Chan, 56.

Terrified to stay put, Chen decided to find a hiding place and went into an empty office.

“I knew if I don’t run, I may get killed,” he said.

Police eventually found Chen on the floor behind a desk, unable to stand up and with his hands raised as officers had demanded. Chen found out when he was being treated at a hospital that colleague Benson Louie, 50, had also been killed. A third driver, Mike Lefiti, 46, also died.

“I keep dreaming every night when I close my eyes, that moment. It’s really scary, I can tell you,” he said. “And you don’t want it to happen next to you and around you. It’s a very, very bad experience.”

Although police have suggested Lam might have felt disrespected by other workers, Chen said it would have been out of character for any of the three men who were killed to have done so.

It would have been especially out of character for Chan and Louie, who were his close friends, Chen said, adding that he knew of no animosity between them and Lam.

“I’m heartbroken. I can’t understand why this happened,” Chen said, a pair of crutches nearby.

A San Francisco Police Department official has said Lam appears to have felt disrespected by co-workers, but did not know if that motivated the shooting.

The officer spoke on condition of anonymity because the officer was not authorized to speak publicly about the investigation.

Chen said Lam never indicated before the shooting that he had problems with other workers, and said he had a friendly chat with Lam about their routes two days before the shooting. They spoke Cantonese to each other, although Lam’s ethnicity is unclear. Records show Lam moved to the United States as an infant from Thailand.

Chen said he does not know how he feels about Lam, although it’s more sadness than anger.

“I’m not even thinking like I hate him or not,” he said. “I’m not.”

(AP)