Wisconsin officials open investigation into fatal police shooting

Officials in the US state of Wisconsin have opened a homicide investigation into the fatal shooting of a man by a police officer.

The police chief in Madison, Wisconsin, told reporters on Thursday that he would cooperate with state investigators. "We will not hide from any aspect of this investigation," John Patterson said.

Police have said that Corey Ruiz, 38, was shot on Wednesday after he pulled out a knife during a struggle with four officers. Bystander footage of the incident has circulated on social media and has sparked protests.

Madison Mayor Satya Rhodes-Conway said the shooting will be "rigorously investigated."

"It does not matter who you are or what your past is; you should not lose your life as a result of an encounter with law enforcement," she said.

The state Justice Department's Criminal Investigation Division will investigate the shooting, since the incident involves police officers. They will also release the name of the officer who fired their weapon, Chief Patterson said.

None of the officers involved in the incident were wearing body cameras at the time.

The incident came after police were called about an individual trying to enter parked vehicles in the neighbourhood, he said.

Ruiz is said to have fled the scene on a bike before officers tracked him down.

Ruiz fell or was pulled from the bike by four officers, and is accused of pulling out a knife and injuring one officer in the melee.