HOUSTON, United States

The man who allegedly shot and killed a Democratic Minnesota lawmaker and her husband and wounded another legislator and his wife was charged with six federal counts of murder, stalking and firearms offenses, according to a criminal complaint released Monday.

Vance Boelter, 57, was charged with two counts of murder for killing Minnesota State Representative Melissa Hortman and her husband, Mark. He was also charged with stalking Hortman and State Senator John Hoffman in addition to two firearms counts in the shooting of Hortman and her husband and Hoffman and his wife, Yvette.

"VANCE LUTHER BOELTER, the defendant, with the intent to kill, injure, harass, intimidate, and place under surveillance with intent to kill, injure, harass, and intimidate another person, used an interactive computer service, electronic communication service, and electronic communication system of interstate commerce...to engage in a course of conduct that placed that person in a reasonable fear of the death of and serious bodily injury to that person and that person’s spouse, and in the course of engaging in such conduct caused the death of that person and that person’s spouse," the FBI said in a charging document.

Boelter is also facing state charges of two counts of second-degree murder and two counts of second-degree attempted murder in the shootings, according to Hennepin County court records.

Hennepin County Attorney Mary Moriarty said during a Monday press conference that she intends to pursue first-degree murder charges against Boelter in the fatal shootings of the Hortmans.

Boelter allegedly posed as a police officer when he carried out the shootings early Saturday morning at both couples' homes, and after a nationwide manhunt, he was captured late Sunday night.

Prosecutors said Boelter carefully planned the attacks by researching the victims and their families, using the internet to find their names and addresses. He then conducted surveillance of their homes and took notes about their locations.

"This was a political assassination, which is not a word we use very often in the United States, let alone here in Minnesota," said acting US Attorney Joe Thompson, in a statement. "It's a chilling attack on our democracy, on our way of life."

"It's no exaggeration to say this is stuff of nightmares," added Thompson.

Prosecutors have not released what punishment Boelter will receive if he is convicted. Minnesota does not have the death penalty and Thompson said it was "too early to tell" whether federal prosecutors will seek the death penalty.