Police say Vance Luther Boelter, 57, is suspected of killing Democratic Minnesota state legislator Melissa Hortman and her husband, and the shooting of State Senator John Hoffman and his wife.
Hortman - the senior Democratic and former assembly speaker in Minnesota - was remembered by Governor Tim Walz as someone with "grace, compassion, and tirelessness."
Among issues she focused on were environmental causes, racial equality, reproductive rights and stricter gun control.
Advocacy groups pointed to her support for police reforms after the 2020 murder of George Floyd, a Black man who died after a Minneapolis police officer knelt on his neck for several minutes. She helped advance a legislation that banned police choke holds.
Walz described the shooting as a "politically motivated assassination.
Former US Vice President Kamala Harris described Hortman as an "outstanding public servant." Harris added: "She passed legislation that enshrined freedoms and increased opportunity for the people of Minnesota. I saw her impact firsthand when I was with her in Minnesota."
Walz said he was cautiously optimistic that Senator Hoffman and his wife would survive "this assassination attempt" as they underwent surgery.
Police responded to reports of gunfire at the Hoffmans' home shortly after 2 am, Champlin police said, and found the couple with multiple gunshot wounds.
After seeing who the victims were, police sent officers to check on Hortman's home. There they encountered what appeared to be a police vehicle and a man dressed as an officer at the door, leaving the house.
"When officers confronted him, the individual immediately fired upon the officers who exchanged gunfire, and the suspect retreated back into the home" and escaped, Brooklyn Park Police Chief Mark Bruley said.
The FBI has offered a reward of up to $50,000 for information that could lead to his arrest.
Boelter had links to evangelical ministries and said he was a security expert with experience in the Gaza Strip and Africa, according to his online postings and public records.
A man who shared a house in Minneapolis with Boelter for a little more than a year, told Reuters he received a text from Boelter on Saturday.
"He said that he might be dead soon," said David Carlson, who called police.
Boelter was appointed in 2016 to the Governor's Workforce Development Board, state records show. The board "has a responsibility to advise the Governor on Minnesota's workforce system," according to its website.
Asked if Boelter knew the Democrat lawmakers, Minnesota Bureau of Criminal Apprehension Superintendent Drew Evans said: "We are still exploring that."
"There's certainly some overlap with some public meetings, I will say, with Senator Hoffman and the individual. But we don't know the nature of the relationship or if they actually knew each other," he told reporters.
Boelter listed himself as having no political party preference, however Carlson said Boelter voted for Trump, was a Christian and did not like abortion, though he added that the pair had not talked about the issue for a long time, adding: "He wasn't really angry about politics."
In social media accounts, public records and websites reviewed by Reuters, Boelter described himself as a Christian minister, a security expert with experience in the Middle East and Africa, and a former employee of food service companies.
He and his wife, Jennifer, also ran a security service called Praetorian Guard Security Services.
Nonprofit tax filings show that Boelter and his wife ran a Christian ministry organisation called Revoformation. The most recent filing, in 2010, lists Boelter as president.
After firing at police on Saturday, the suspect abandoned a vehicle in which officers found a "manifesto" and a list of other legislators and officials, law enforcement officials said.
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