Slaying suspect surrenders in Martinez after standoff

An 18-hour standoff with a suspect in the fatal Walnut Creek shooting of a 47-year-old woman he had dated ended Friday afternoon with the man in custody, police said.

The standoff in Martinez began about 7 p.m. Thursday — more than five hours after the suspect allegedly fled the scene of the killing — when authorities surrounded a silver Mercedes with 38-year-old Gregory Prokopowicz inside, officials said.

Police said the woman, identified as Roselyn Policarpio of Martinez or Stockton, was killed about 1:30 p.m. Thursday in the 1900 block of First Avenue in Walnut Creek.

Prokopowicz, who held a gun to his head and at one point inadvertently discharged a round through his windshield, finally stepped out of the car with his hands up shortly before 1:20 p.m. Friday, police said, but a less-lethal projectile was fired at him — injuring his ribs — and he re-entered the car. He could then be seen dropping a gun out of the window.

Walnut Creek police Lt. Tom Cashion said Prokopowicz, who has past addresses in Martinez and Walnut Creek, was in custody at 2:14 p.m. During negotiations, Martinez police closed streets and asked some residents to shelter in place. Filipa Ioannou and Michael Bodley are San Francisco Chronicle staff writers. Email: fioannou@ sfchronicle.com, mbodley@ sfchronicle.com Twitter: @obioannoukenobi, @michael_bodley