A massive manhunt entered a second day on Sunday in Minnesota for the suspected gunman who killed a Democratic state lawmaker while posing as a police officer — a crime that Governor Tim Walz characterized as a "politically motivated assassination."

The suspect, whom police have identified as Vance Luther Boelter, 57, fled on foot when officers confronted him at the Brooklyn Park home of former Minnesota House Speaker Melissa Hortman and her husband, Mark, who were both killed.

The gunman earlier had shot and wounded another Democratic lawmaker, state Sen. John Hoffman, and his wife Yvette at their home a few kilometres away, authorities said.

Minnesota U.S. Sen. Amy Klobuchar, a Democrat, said on Sunday morning that authorities believe the suspect is still in the Midwest, adding that an alert had been put out in neighbouring South Dakota.

"Clearly, this is politically motivated," she said, noting that the state's entire congressional delegation — Republicans and Democrats — issued a shared statement condemning the shootings.

The suspect left behind a vehicle outside Hortman's house in suburban Minneapolis that resembled a police SUV, including flashing lights, and contained a "manifesto" and a target list of other politicians and institutions, officials said.

Authorities had not publicly identified a specific motive as of Saturday evening.

Boelter has links to evangelical ministries and claimed to be a security expert with experience in the Gaza Strip and Africa, according to online postings and public records reviewed by Reuters.

"There clearly was some through line with abortion, because of the groups that were on the list and other things that I've heard were in this manifesto. So that was one of his motivations," Klobuchar said.

Boelter had been appointed in 2016 by Walz's predecessor to a state advisory board, where he served alongside Hoffman, according to state records. Authorities said they were not certain yet whether the two had any meaningful interactions.

"There's certainly some overlap with some public meetings, I will say, with Senator Hoffman and the individual," Minnesota Bureau of Criminal Apprehension Supt. Drew Evans told reporters on Saturday.

"But we don't know the nature of the relationship or if they actually knew each other."

The killing was the latest in a series of high-profile episodes of political violence, including the attack on former Democratic U.S. House Speaker Nancy Pelosi's husband in 2022, the attempted assassination of Donald Trump during last year's presidential campaign, and an arson attack at Pennsylvania Gov. Josh Shapiro's house in April.

Republican and Democratic politicians across the country reacted with shock and horror and issued calls to tone down increasingly heated political rhetoric.

Klobuchar said she had seen both Hortman and Hoffman at a political dinner on Friday, just hours before they were shot.

"We started out together in politics, moms with young kids, and somehow she was able to balance getting to know every door, knock on every house in her district, while raising two children — Girl Scout leader, she taught Sunday school," she said of Hortman, 55.

Klobuchar said both Hoffmans were "hanging in there" after undergoing surgery for multiple gunshot wounds.

Gunman posed as officer

The attacks started around 2 a.m. ET on Saturday, when authorities said a gunman shot the Hoffmans in their home in Champlin, before driving several kilometres to Hortman's home in Brooklyn Park.

Police went to the Hortman house proactively at the request of a sergeant who responded to the Hoffman attack, concerned other politicians might be at risk. The gunman immediately fired upon the two officers when they arrived, and when they returned fire, he ran.

The FBI released photos of the suspect wearing a rubber mask and a police-like uniform.

David Carlson, 59, told Reuters he has shared a house in Minneapolis with Boelter for more than a year and last saw him on Friday night. He said he received a disturbing text from Boelter at about 6 a.m. on Saturday.

"He said that he might be dead soon," said Carlson, who called police.

WATCH | Gunman posed as police officer, authorities say:

Ex-Minnesota House Speaker and husband dead in targeted shootings, second lawmaker and wife wounded

Former state House Speaker Melissa Hortman and her husband were killed by someone posing as a police officer on Saturday, and a second lawmaker and his wife were shot and wounded in what Minnesota Gov. Tim Walz said were politically motivated shootings.

Police said they found flyers with "No Kings" printed on them in the suspect's car in reference to the thousands of nationwide "No Kings" protests on Saturday against the Trump administration, but that there were no known direct links between him and the movement.

"Such horrific violence will not be tolerated in the United States of America," Trump said in a statement.

Trump has faced criticism from some opponents for using inflammatory rhetoric at times when talking about his political rivals.

In one of his first moves in office earlier this year, Trump pardoned nearly everyone criminally charged with participating in the Jan. 6, 2021, Capitol attack.