A gunman posing as a police officer killed a senior Democratic state assemblywoman and her husband on Saturday in an apparent "politically motivated assassination," and wounded a second lawmaker and his spouse, Minnesota Gov. Tim Walz and law enforcement officials said.

A major search backed by the FBI was underway for the suspect, who fled on foot after firing at police and abandoning a vehicle in which officers found a "manifesto" and a list of other legislators and officials, law enforcement officials said.

The suspect was identified as 57-year-old Vance Luther Boelter, Minnesota Bureau of Criminal Apprehension Superintendent Drew Evans told a news briefing.