The sheriff’s office has been able to track at least 40 successful thefts to groups coming to Jefferson County from St. Louis and north St. Louis County, and suspects dozens more may be connected to the groups, Marshak said. He did not specify how investigators determined where the thieves were coming from, but said he was not speculating: His department has found at least two or three coordinated groups that have driven into the county repeatedly to steal from unlocked cars.

“We’re making it easy for them,” Marshak said, adding that the thieves have made off with firearms, credit cards, checks and purses in the thefts. No arrests have been made, but the sheriff said his office has identified suspects.

Marshak said Friday’s shooting shows how theft from cars has gotten more serious than it once was in Jefferson County and surrounding areas, changing from a random crime to an organized one.

He warned residents to lock their cars and call the sheriff’s office if they spot someone checking car doors in neighborhoods.

Marshak also warned residents to be careful if they encounter the thieves.

“If they’re willing to produce a firearm, take aim and attempt to murder someone, this is serious business,” he said. “And we want to make sure our community is aware.”