A gunman killed two police officers and three city officials on Thursday night when he stormed into a city council meeting in a suburb of St. Louis, police said.
The gunman, who was later shot dead by police, was identified by witnesses as 52-year-old Charles "Cookie" Thornton, a contractor in a feud with local officials. Police declined to confirm his identity.
He killed one police officer in the parking lot outside the city hall building in Kirkwood, Missouri, before rushing in as the meeting was getting under way.
"He kept saying something about, 'Shoot the mayor' and he just walked around shooting anybody he could," said Janet McNichols, a reporter covering the meeting for the St. Louis Post-Dispatch newspaper.
Police said he shot dead a second police officer, and three two council members and a city engineer.
A city attorney fended off the gunman by throwing chairs at him, according to witnesses at the meeting that was attended by roughly 30 people.
Kirkwood Mayor Mike Swoboda was shot in the head and was in critical condition and another reporter suffered a hand wound.
Thornton was well-known for his erratic behaviour in Kirkwood, an upscale suburb of 25,000 people about 15 miles (24 km) southwest of St. Louis.
He was convicted in 2006 of disorderly conduct after twice disrupting city council meetings. Thornton had complained that his contracting business was being harassed by city officials and at one meeting he repeatedly called Mayor Swoboda a "jackass" before being hauled away.
Swoboda, the mayor since 2000 and a council member dating to 1976, was due to leave office within months.
After the shooting, local television station KMOV-TV interviewed Gerald Thornton, the gunman's brother.
"My brother went to war tonight with the people and government that were putting torment and strife into his life and he ended it," Gerald Thornton said. "I'm OK with it."
A lawsuit by Thornton charging that his constitutional rights of free speech were violated at the meetings was dismissed last month by a federal judge.
Mass shootings are not particularly rare in the United States. In December, a 19-year-old gunman in Omaha, Nebraska, killed eight people and then himself at a shopping mall, and on Saturday a man robbing a clothing store outside Chicago shot five women to death. He has not yet been caught.
