San Francisco Assistant Chief of Police Toney Chaplin points to take a question at a news conference near a UPS package delivery warehouse where a shooting took place Wednesday, June 14, 2017, in San... (Associated Press) 
 
 SAN FRANCISCO (AP) — A United Parcel Service driver who opened fire during a meeting with co-workers had filed a grievance that he was working excessive overtime and appeared to specifically go after the three drivers he killed before fatally shooting himself. 
 
 Jimmy Lam, 38, filed the grievance in March complaining of too much overtime and requesting that the package delivery company relieve him of working extra hours going forward, Joseph Cilia, an official with a Teamsters Union local that represents UPS workers in San Francisco, told The Associated Press. 
 
 During a Wednesday morning meeting, Lam walked up to driver Benson Louie and shot him. As his co-workers frantically fled the room, he shot Wayne Chan in the back, and then walked up to him and "finished him." Mike Lefiti was fleeing from the building when Lam went out onto the street and shot him, Cilia said witnesses told him. 
 
 "It's senseless. I can't think of anything. Why him? Why them?" Cilia asked. "I can't put it together." 
 
 Officials late Wednesday confirmed San Francisco residents Louie, 50, and Chan, 56, and 46-year-old Lefiti, of Hercules, were killed in the shooting. 
 
 Two other UPS employees were wounded, but Cilia said both were released from the hospital. 
 
 Amid a barrage of gunfire, some workers sought refuge on the roof of the four-story facility, while others ran outside and pounded on the windows of a public bus, witnesses said. 
 
 "They were screaming, 'Go! Go! Go!'" said Jessica Franklin, 30, who was riding to work when the bus made a regular stop in front of the UPS facility. "As they got on the bus, they were all ducking." 
 
 Auto shop owner Robert Kim said he saw "a mob of UPS drivers" running down the street screaming "Shooter! Shooter!" 
 
 The shooting prompted a massive police response in one of the city's industrial neighborhoods, about 2 miles (3 kilometers) from downtown San Francisco, Assistant Police Chief Toney Chaplin told reporters. 
 
 UPS spokesman Steve Gaut said the shooter was a company employee. A San Francisco Police Department official identified Lam, 38, and said he's from San Francisco but had no immediate details on his background. 
 
 The official spoke on condition of anonymity because the investigation is ongoing. 
 
 Lefiti's cousin, Mack Toia, told KGO-TV (http://abc7ne.ws/2sch61d) he was at the UPS facility waiting to pick up Lefiti when shots rang out. He left his van and saw his cousin sprawled on concrete behind a gate, Toia said. 
 
 "The police officers were right on the scene just like that. I got to touch him, but I couldn't hug him," Toia said. "They just pushed me away because they were trying to resuscitate him." 
 
 Co-worker Isaiah Miggins said he saw Lefiti, known as "Big Mike," as he arrived for work just before 9 a.m., a few minutes before the shooting started. "He was a joyful man. Always happy," Miggins said. 
 
 On social media, heartbroken family members of Lefiti recalled him as a warm-spirited man devoted to his children and family. A photo on his Facebook page shows Lefiti in his brown UPS uniform holding a trophy. He also posted photos of his UPS truck and an award for 15 years of service to the company in 2015. 
 
 Chaplin said police have not determined a motive. 
 
 A 30-year-old tech worker who lives across the street from the warehouse said he heard up to eight gunshots. 
 
 "They were all in rapid succession," said Raymond Deng. "It was like tat, tat, tat, tat, tat, tat, tat." 
 
 Deng watched from his window in the Potrero Hill section of San Francisco as workers fled the building. He said another group of about 10 people gathered on the roof and held up their hands waving for help. 
 
 "I saw police officers go up from the ramp and then storm the buildings," he said. "It's crazy." 
 
 Officers found two victims outside and others inside and pulled the wounded to safety as they confronted the gunman, who was armed with an "assault pistol," Chaplin said. 
 
 "The suspect put the gun to his head and discharged the weapon," Chaplin said, adding that police did not fire any shots. Two guns were recovered at the scene, he said. 
 
 The shooting occurred the same day a gunman opened fire on Republican lawmakers at a congressional baseball practice in Virginia, wounding U.S. Rep. Steve Scalise of Louisiana and several others. 
 
 ___ 
 
 AP writers Janie Har, Jocelyn Gecker and Linda Wang in San Francisco and Mike Balsamo in Los Angeles contributed to this story. 

 Police identify UPS gunman as SF man 
 
 San Francisco police were digging into the past of a United Parcel Service employee as they tried to figure out why he allegedly killed three co-workers at a company distribution center before shooting himself to death Wednesday. 
 
 The San Francisco Police Department identified the shooter as Jimmy Lam, 38, of San Francisco. They seized Lam’s BMW, which was parked near the shooting scene, and raided his home in San Francisco’s Inner Richmond neighborhood, where neighbors said he mostly kept to himself. 
 
 Workers at the UPS building at 320 San Bruno Ave. said the gunman was a fellow employee, and Assistant Police Chief Toney Chaplin said the shooter was wearing a UPS uniform. 
 
 A union official said Lam had filed a grievance complaining that he was working excessive overtime, according to the Associated Press. 
 
 Lam’s neighbors said they often saw him walking around in a company uniform, looking at his phone and smoking a cigarette. 
 
 In the afternoon, officers left his home — one of two units in a grayish-green building — with what appeared to be a computer, several bags of evidence and a file box. Around the same time, police towed away a black 2012 BMW coupe registered to Lam that had been parked near the shooting scene. 
 
 “I’m a little creeped out,” said Jennifer Plog, who lives next door to Lam’s home and said he had appeared harmless. “It’s creepy knowing that people next door have the ability to have guns and shoot people they work with. It makes me feel unsafe.” 
 
 No one interviewed in the neighborhood of two-story homes and apartments said they had spoken with Lam. 
 
 According to court records, Lam’s only brushes with the law involved driving. In 2010, he was convicted of driving under the influence and was placed on probation after San Francisco police said he crashed into parked vehicles. He allegedly had neither a valid license nor insurance. 
 
 Three years later, city prosecutors filed a motion to revoke his probation when he was arrested again for driving under the influence. 
 
 Police officials said they recovered two guns from the scene of the shooting, including what they described as an assault pistol. They did not provide further details or say where the guns had come from or whether they had been legally purchased. 
 
 The shooting happened at 8:55 a.m. as UPS workers gathered for a regular meeting called Wednesday Wellness, causing panic as employees dived to the ground or ran for safety. In addition to killing three, the gunman wounded at least two others, while three people were injured while fleeing, officials said. 
 
 When responding police officers encountered the suspect inside the building, officials said, he raised a pistol to his head and pulled the trigger. 
 
 Vivian Ho and Michael Cabanatuan are San Francisco Chronicle reporters. Email: vho@sfchronicle, mcabanatuan@sfchronicle.com. Twitter: @VivianHo @ctuan
– Though motive has not been established, the UPS driver who opened fire during a meeting with co-workers had filed a grievance that he was working excessive overtime and appeared to specifically go after the three drivers he killed before fatally shooting himself. Jimmy Lam, 38, filed the grievance in March complaining of too much overtime and requesting that the package delivery company relieve him of working extra hours going forward, Joseph Cilia, an official with a Teamsters Union local that represents UPS workers in San Francisco, tells the AP. During a Wednesday morning meeting, Lam walked up to driver Benson Louie and shot him. As his co-workers frantically fled the room, he shot Wayne Chan in the back, and then walked up to him and "finished him." Mike Lefiti was fleeing the building when Lam went out onto the street and shot him, Cilia says witnesses told him. "It's senseless. I can't think of anything. Why him? Why them?" Cilia asked. "I can't put it together." Officials late Wednesday confirmed San Francisco residents Louie, 50, and Chan, 56, and 46-year-old Lefiti, of Hercules, were killed in the shooting. Two other UPS employees were wounded, but Cilia says both were released from the hospital. As for Lam, "the suspect put the gun to his head and discharged the weapon," says Assistant Police Chief Toney Chaplin, adding that police did not fire any shots. Two guns were recovered at the scene, and SFGate reports one was an assault pistol. It adds that police towed a 2012 BMW from the scene and removed a computer and other potential evidence from Lam's home.