Washington DC - The suspected killer of a Minnesota lawmaker could face the death penalty, US prosecutors said Monday as they revealed chilling details of an alleged murderous nighttime spree targeting local Democrats.

Vance Boelter (57) faces six federal charges, including two counts of murder by firearm, punishable by life imprisonment or the death penalty, acting US Attorney for the District of Minnesota Joe Thompson told a press conference in Minneapolis.

Thompson gave a shocking account of Boelter's alleged activities in the early hours of Saturday, revealing that he went to the homes of four state politicians – all of them Democrats – and not only the two previously reported.

"It is no exaggeration to say his crimes are the stuff of nightmares. Boelter stalked his victims like prey. He went to their homes, held himself out as a police officer, and shot them in cold blood," the US attorney said.

Murder Suspect in assassination of Minnesota Democratic lawmaker caught after manhunt

The rampage began with the shooting of state Senator John Hoffman and his wife and ended with the killing of Representative Melissa Hortman and her husband. But it had two other stops in between, Thompson said.

Clad in a black tactical vest, body armor, and a silicon mask, he banged on the door of a politician's home in the Minneapolis suburb of Maple Grove, but found no one home, Thompson said.

He then traveled to a home in the adjacent town of New Hope, but left after he was spotted by a police officer, Thompson said, adding that proactive "wellness checks" on state legislators by local police had prevented more deaths.

After a 48-hour manhunt, Boelter was taken into custody in a rural area about an hour southwest of Minneapolis, police and state officials said.

SWAT teams used drones to identify the suspect's location, and officers crawled through ditches in the area's farm fields to confine him, the Minnesota Star Tribune reported.

The suspect was due to appear in a federal court in Saint Paul, Minnesota at 1:30 PM local time (1830 GMT). Minnesota state officials earlier announced they would pursue first-degree murder charges against Boelter.