Alan Eugene Miller was arrested shortly after the shootings when police pulled him over on nearby Interstate 65. He briefly struggled with officers, and a gun was found in his car, police said.
Police arrived at the Ferguson offices at 7:04 a.m. The two victims were identified as Lee Holbrooks and Christopher Yancy.
Officers were still securing the crime scene 13 minutes later when dispatchers got a second emergency call, this time about the shooting of Terry Jarvis at Post Airgas, a company that sells helium, oxygen and other gases several miles from Ferguson.
"We are deeply saddened by this act of senseless violence," said a Ferguson spokesperson in a written statement. "We are greatly appreciative of the support and assistance we have received from the police and the community, and we are cooperating fully with the police investigation.
"Our prayers and condolences are with the families of the victims. Our focus is to do all that we can to support the families of our slain associates and other associates at our Pelham location."