SUISUN CITY -- Police were investigating why someone shot and killed a 21-year-old man as he walked home early Sunday morning, police said Wednesday.

Gary T. Summers Jr., 21, of Suisun City, was found on the sidewalk in the 1000 block of Pintail Drive at about 3:45 a.m.

He was wearing a red hat and was not a known gang member, but police are not discounting the possibility he shot because he was assumed to be a gang member, Sgt. David Kasid said.

"This may be a case of being in the wrong place at the wrong time," Kasid said.

Kasid said police had minor, non-criminal contact with Summers previously. Kasid said he had warned Summers about the dangers of walking alone at night.

Summers did not have a car and was unemployed, Kasid said. It's believed he was visiting friends in Fairfield and was walking home when he was shot about half a mile from his residence, Kasid said.

An autopsy Tuesday determined Summers was shot with a small-caliber gun, Kasid said.

Police are asking for the public's help in solving the case. Anyone with information is asked to call (707) 421-7390.