UNION CITY — Police arrested a 15-year-old boy Friday morning, but were still looking for two other people believed to be involved in a shooting earlier this week that left a 19-year-old man in critical condition.

The boy, whose name was not released, was found inside a home near 11th and G streets in the Decoto neighborhood, where Union City and Newark SWAT teams were conducting a search, police Lt. Kelly Musgrove said.

The boy was arrested on suspicion of attempted murder stemming from the shooting, which occurred on Mission Boulevard near Whipple Road.

The 19-year-old was shot in the back with multiple weapons — including a shotgun — about 10:15 p.m. Wednesday as he walked past a group of three people, Musgrove said.

The victim told police that he briefly looked back over his shoulder at the group, and seconds later they began firing at him. Police said they have not yet established a motive.

Witnesses said the gunmen fled on foot.

Authorities said Friday that community members helped investigators identify the 15-year-old.

Police said they recovered evidence from the boy's home, but did not specify if that included any weapons.

Anyone with information may call police at 510-471-1365.

Reach Ben Aguirre Jr. at 510-353-7011. Read his blog at www.ibabuzz.com/tricitybeat, and twitter feed at www.twitter.com/benaguirrejr.