Vallejo police were investigating the fatal shooting of a man in the Country Club Crest neighborhood of North Vallejo on Saturday afternoon.
The killing in the residential 100 block of Simonton Street took place about 4 p.m. as trick-or-treaters prepared to go out on for Halloween.
The shooter fled before police arrived and was still at large, a department spokesman said.
It was the 12th homicide of the year in Vallejo, police said.
Anyone with information was asked to contact Detective Zach Horton at 707-648-5425 or Zach.Horton@cityofvallejo.net, or Detective Seamus Lanham at 707-648-4514 or Seamus.Lanham@cityofvallejo.net.