DUBLIN -- BART Police Sgt. Tom Smith Jr. conducted many searches during his 23 years in law enforcement. So when the department's top detective on Tuesday entered a tiny one-bedroom apartment of a robbery suspect who was already in jail, there was no reason to believe this would be his last.
Smith wore a bulletproof vest beneath his plain clothes as he and four other officers found the door unlocked and stepped inside with guns drawn -- just in case someone was home.
Moments later, Smith lay dying, felled by another officer's bullet.
On Wednesday, while investigators explained more about what happened before Smith's tragic death, they refused to address what went so horribly wrong inside the Dublin apartment -- particularly whether the other officer mistook Smith for a threat or if his handgun went off accidentally. One expert deemed the latter unlikely.
One or more of the officers inside might have been wearing a camera, but investigators wouldn't say whether the shooting was recorded.
Only the terrible toll on Wednesday was clear: Smith, 42, was the first officer killed in the line of duty in the BART Police's 42-year history, leaving behind his wife, Kellie -- also a BART officer he met on the job -- and their 6-year-old daughter.
"The department is grieving, in shock. Please give us time," BART Police Chief Kenton Rainey said at a tearful news conference Wednesday in Oakland, describing Smith as a can-do, happy family man. "You just couldn't meet a nicer guy."
Ironically, Smith played a key role in helping the BART Police get better training and rebuild its community ties after the calamitous 2009 fatal shooting of prone, unarmed passenger Oscar Grant III at Oakland's Fruitvale station. He also was called on to explain another BART officer's fatal shooting of a homeless man in 2011 to a citizen advisory board.
Now BART Police will be left to explain how a man who spent more than half his life with the department was killed by a fellow officer.
BART officers were stationed outside Smith's San Ramon home early Wednesday and also at the East Bay home of Officer Michael Maes, who sources said is the colleague who shot Smith. An officer outside Maes' home said the family would not comment and asked that the family's privacy be respected.
Rainey refused Wednesday to name the officer who fired the fatal shot, in order to give him time to grieve. "He's extremely upset," Rainey said.
The Alameda County Sheriff's Office, which is investigating the shooting, also refused to release the other officer's name but noted he had more than 10 years experience. Moraga Police confirmed Maes worked there from 1988 to 2000, when he left to join BART.
Sheriff's Sgt. J.D. Nelson said seven BART officers and a Dublin police officer converged on the robbery suspect's apartment, in the Park Sierra complex at 6450 Dougherty Road, just before 2 p.m. Tuesday. They knocked twice on the door, but nobody answered; the door was unlocked, so five BART officers, including Smith, stepped in. Because the suspect was already on probation for another crime, police didn't need a warrant to search his home.
Nelson would not disclose what happened next, except to say one of the officers fired a single shot, wounding Smith in the upper body. Smith died later Tuesday at Eden Medical Center in Castro Valley; an autopsy was performed Wednesday, but no details were immediately available.
Rainey said all uniformed BART officers up to the rank of sergeant must wear cameras on their lapels, but that's optional for plainclothes detectives. The cameras became mandatory as one of several reform measures adopted after the Oscar Grant shooting, but neither Rainey nor Nelson said whether those required to wear cameras had actually done so Tuesday.
"Our officers are trained to conduct this type of incident: going out, doing a probation search of an individual who was wanted for committing crimes on BART property," Rainey said, adding such searches aren't uncommon. "They're supposed to practice good officer safety and in accordance with their training ... because you never know what's on the other side of the door."
Entering a home is the "most dangerous" type of work police do, he added. "There is nothing routine about it."
Rainey said BART officers typically carry a 10 mm Glock or a .40-caliber Sig Sauer semi-automatic handgun, although some are authorized to carry other weapons. Nelson would not say what type was used in the shooting. Tom Nolan, criminal justice chairman at State Univeristy of New York at Plattsburgh, said police-issued firearms generally don't accidentally discharge.
"You don't just drop one on the floor and have it accidentally go off," said Nolan, who retired after 27 years as a Boston police officer. "You have to affirmatively pull the trigger, and it takes about five pounds of pressure to do so."
This could've been a case of target misidentification, poor communication, ineffective training or lack of coordinated effort, he said. "This is too rookie of a mistake for officers with that amount of experience on the job. These are routine searches. It's not something extraordinary."
The police were right to draw their guns if they didn't know who was inside, Nolan said, "but I would expect their fingers would be outside the trigger guard because that's what they're trained to do. You're trained to keep your finger outside the trigger guard to avoid certain situations like this tragic one."
Smith is the 36th on-duty officer killed by accidental gunfire in California since 1895, and the first since two Oakland police officers mistakenly shot and killed an undercover detective in January 2001. Gov. Jerry Brown and state Attorney General Kamala Harris offered their condolences Wednesday morning.
The robbery suspect, John Henry Lee, 20, pleaded not guilty on Wednesday to one count of second-degree robbery with use of a handgun.
According to a declaration written by Maes and filed in Alameda County Superior Court, Lee leveled a gun as he robbed a man of his wallet, phone and laptop bag in Oakland's Fruitvale BART station's parking structure on the morning of Jan. 15. Less than a day later, a San Leandro officer saw Lee with a stolen car and burglarizing another car; Lee fled but later crashed and was caught with help from a police dog. He has been in jail since last Thursday.
On Wednesday morning, a trail of blood droplets led up to the front door of the apartment unit where Tuesday's shooting occurred. A man who answered the apartment's door refused to comment or identify himself.
Staff writers David DeBolt, Matt O'Brien, Malaika Fraley, Rick Hurd, Katie Nelson and Jeremy Thomas contributed to this report. Contact Josh Richman at 510-208-6428; follow him at Twitter.com/josh_richman.