MINNEAPOLIS, Minnesota - The suspect accused of assassinating a Minnesota lawmaker and shooting another this weekend drove to the homes of at least four state politicians as part of a planned killing spree, US authorities said on Monday.

Vance Boelter, 57, faces state and federal murder charges after his arrest on Sunday night following a massive two-day manhunt that was the largest in state history.

He is accused of fatally shooting Melissa Hortman, the top Democrat in the Minnesota House, and her husband Mark, in their home on Saturday. Boelter is also charged with shooting and wounding Democratic lawmaker, state Senator John Hoffman, and his wife Yvette, in their home a few miles away.

Prosecutors said on Monday that Boelter visited the homes of two other lawmakers disguised as a police officer, hunting more targets. Investigators said they recovered notebooks from his car and residence that included the names of dozens of Democratic legislators, along with abortion rights advocates.

They also revealed that he sent a text to his family hours after the shooting that said in part, "Dad went to war last night."

"Political assassinations are rare," Joseph Thompson, Minnesota's acting US attorney, said at a news conference. "They strike at the very core of our democracy."

Thompson said a precise motive was not yet clear. Contrary to earlier news reports, authorities have not discovered a "Unabomber-style manifesto," he said.

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The killings unfolded against a backdrop of increasing political violence in the US in an era of extreme social and political polarization.

President Donald Trump was the target of two assassination attempts during his campaign last year, including at a Pennsylvania rally that left him with a wounded ear and killed one bystander. In April, a man broke into the home of Pennsylvania Governor Josh Shapiro and set it on fire while Shapiro and his family were asleep.

Boelter made a brief appearance in St. Paul federal court on Monday to face murder and other charges, which could result in the death penalty. Wearing an orange jumpsuit, he told a judge he understood the charges against him and remained composed throughout the 15-minute hearing.

He did not enter a plea and will return to court on June 27. Boelter's court-appointed attorney, Matthew Deates, declined to comment after the hearing. Boelter also faces separate state murder charges in Hennepin County.

'Campaign of violence'

Political tensions were already high on Saturday. Mass protests against Trump's agenda took place across the country, fueled in part by the deployment of US Marines and National Guard troops over immigration protests in Los Angeles and a military parade in Washington on the president's birthday.

"Vance Luther Boelter embarked on a planned campaign of stalking and violence, designed to inflict fear, injure and kill members of the Minnesota state legislature and their families," an FBI affidavit unsealed on Monday read.

The attacks began around 2 am on Saturday, when a gunman wearing a police-style tactical vest and a "hyper-realistic silicone mask" knocked on the Hoffmans' door in Champlin, announced himself as a police officer and then shot the couple multiple times, according to prosecutors.

He was driving an SUV outfitted with police-style lights and a fake license plate that read "POLICE."

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Boelter then traveled to the home of another state lawmaker in Maple Grove, where he rang the doorbell at 2:24 am, Thompson said. The official, whom prosecutors did not name, was not home.

Boelter also visited the home of an unnamed state senator in New Hope, prosecutors said. A officer dispatched to the house to check on the senator after the Hoffman shooting saw Boelter parked outside and believed he was another police officer.

When Boelter ignored the officer's greeting, the officer went to the door to wait for additional police, Thompson said. Boelter had left by the time they arrived.

Shortly after, police went to the Hortmans' house in Brooklyn Park as a precaution. The arriving officers saw the suspect shoot Mark Hortman through an open door around 3:35 am and exchanged fire with him before he fled out the back, according to prosecutors.

Melissa Hortman was found dead inside.

When police searched Boelter's SUV, they discovered three assault-style rifles, a handgun, a gold police-style badge and a target list, according to authorities.

Boelter's notebooks showed he had planned the attacks for some time. He had the names and, in some cases, home addresses for more than 45 elected officials, "mostly or all Democrats," according to the affidavit.

In one book, Boelter noted the Hortmans had two children and added surveillance details about their house, writing, "Big house off golf course 2 ways in to watch from one spot," the affidavit said.

Massive manhunt

Boelter's wife and other family members received a text message at 6:18 am that read, "Dad went to war last night... I don't wanna say more because I don't wanna implicate anybody," according to the affidavit. A second text warned them to leave the house because some "armed and trigger-happy" people were coming.

Boelter's wife also consented to a search of her car, which turned up two handguns, about $10,000 cash and passports for family members, who were in the car when police came to the house, the affidavit said.

Authorities said the investigation would determine if Boelter's wife had any role in, or was aware of, the suspect's plan beforehand. He has five children, according to media reports.

Around 7 am on Saturday, Boelter encountered someone at a bus stop in Minneapolis and eventually offered to buy his Buick, according to prosecutors.

Investigators on Sunday found the Buick in rural Sibley County about an hour's drive from Minneapolis, near Boelter's listed home address. Inside the car, officers found a handwritten letter to the FBI, in which Boelter gave his name and admitted to the shootings, according to the affidavit.

More than 20 SWAT teams combed the area, aided by surveillance aircraft. Boelter, who was armed, crawled from a wooded area and surrendered to police in a field.

Minnesota US Senator Amy Klobuchar shared on social media a text from Yvette Hoffman on Sunday that said her husband had been shot nine times, while she was shot eight times.

"We are both incredibly lucky to be alive," Yvette Hoffman wrote. "We are gutted and devastated by the loss of Melissa and Mark."