The suspected killer of a Minnesota lawmaker went to four state politicians' homes on the night that he shot dead one and wounded another, a US attorney said Monday.

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

The murderous nighttime spree 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 travelled to a home in the adjacent town of New Hope, but left after he was spotted by a police officer.  

"The details of Boelter's crimes are truly chilling. They are the stuff of nightmares," Thompson said.

Boelter, 57, was taken into custody late Sunday in a rural area about an hour southwest of the Minneapolis suburbs where the killings occurred, 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.