A man who is accused of killing a Democratic state lawmaker and her husband, and injuring another state lawmaker and his wife, allegedly attempted to kill two other state lawmakers, Minnesota officials said on Monday.

Vance Luther Boelter, 57, who is charged with fatally shooting Melissa Hortman, a Minnesota Democrat, and her husband, Mark, visited the homes of three other state lawmakers in "truly chilling" attacks, US Attorney Joseph H Thompson said.

Mr Boelter, who police said researched the victims and their families beforehand, allegedly had planned for a larger scale attack, which police thwarted.

He appeared in court on Monday afternoon to face six federal charges, and possibly the death penalty, if he is found guilty.

Mr Boelter was wearing an orange jumpsuit when he arrived in court in St. Paul on Monday afternoon. He said he cannot afford a lawyer and will have a federal defence lawyer.

At the brief hearing, Mr Boelter said he has seven cars, $20,000-30,000 in savings and makes about $540 per week.

At a press conference on Monday officials walked through the early hours of Saturday morning in the suburbs of Minneapolis when the Hortmans were killed, and John Hoffman, a Minnesota state senator, and his wife, Yvette Hoffman, were shot multiple times.

They also announced that Mr Boelter faces six federal charges, some of which make him eligible for the death penalty. At the federal level, he faces two counts of stalking, two counts of murder, and two firearms-related charges.

Separately, at the state level Mr Boelter is charged with two counts of second-degree murder and two counts of attempted second-degree murder at the state level.

Thompson said that Mr Boelter arrived at the Hoffman home disguised as a police officer in a large black car with emergency lights on the vehicle. Mr Boelter was wearing a "hyper realistic silicon mask" when he rang the doorbell and shouted "this is the police, open the door".

Thompson said authorities have a clear picture of what happened because the Hoffmans have a security camera outside their front door.

When the Hoffmans opened the door, Mr Boelter shined a flashlight at the couple. Mr Boelter told the couple there was a shooting reported in the house and lowered his flashlight, Thompson said. The couple then realized he was not a police officer.

After they attempted to push him out, he allegedly fired at the couple multiple times, Thompson said, then fled the scene and the couple's daughter Hope called 911.

Yvette Hoffman was shot eight times and John Hoffman was shot nine times. Both remain in hospital, though Minnesota Governor Tim Walz has said they are expected to make a full recovery.

After allegedly shooting the Hoffmans, Mr Boelter drove to another state representative's home and rang the doorbell there, Thompson said.

That state representative was not home, Thompson said, noting that she and her family were on vacation. Authorities did not reveal her name.

He then drove to a third lawmaker's home, allegedly targeting them, Thompson said. Officials did not reveal the name of that state lawmaker, either.

Thompson said an officer pulled up next to Mr Boelter in his vehicle and assumed he was a police officer, dispatched to the scene to perform a wellness check on that lawmaker.

When the officer asked Mr Boelter what he was doing, he simply stared straight ahead, Thompson said, and Mr Boelter went on to the Hortman residence.

He is accused of arriving at the Hortman home, and allegedly shooting and killing Melissa and Mark Hortman. Police said they found him at that residence and engaged fire before Mr Boelter fled.

After he fled, police embarked on a two-day search for Mr Boelter before finding him late Sunday night in a wooded rural area west of Minneapolis, where he surrendered peacefully, eventually crawling towards officers, police said.

Thompson said Mr Boelter had "planned his attack carefully".

"He conducted surveillance of their homes and took notes about the location of their homes," he said of Boelter.

Upon finding his car, officials discovered five more firearms including assault-style rifles, large quantities of ammunition and a list of more than 45 Minnesota state and federal elected officials, including Melissa Hortman.

Mark Bruley, police chief from Brooklyn Park, Minnesota, said the officers who arrived at the Hortman home "foiled" a larger plan. They "essentially took (Mr Boelter's) vehicle away from him, which involved all his maps, all his names, all his weaponry", Mr Bruley said.

"I would be very scared what it would look like over the next few hours ahead had we not done that," he said.

"It's a chilling attack on our democracy, on our way of life," Thompson said at the Monday press conference. "It's only the most recent example of violent political extremism in this country, and that's a trend that's been increasing over in recent years, and that's unfortunate.

I hope it is a wake up call to everyone that people can disagree with you without being evil or needing to be killed or hurt."

Mr Boelter is scheduled to return to court for his next hearing 27 June. (BBC)

Update news