Investigators are trying to determine what led a gunman to open fire on two utility workers in a residential neighborhood in St. Louis, killing both of them before fatally shooting himself.

Police say the gunman walked up to the two men who worked for Laclede Gas on Thursday morning and started shooting, then turned the gun on himself. Police Capt. Mary Warnecke said, "It does not appear words were exchanged."

Both Laclede Gas and the electric company Ameren Missouri pulled workers from the streets for the rest of the day as a precaution.

Police described the St. Louis shooter as black, and both victims as white, but there was no indication the shooting was racially motivated.

The names of the shooter and the men he killed have not been released.