US police say a man has confessed to killing four people, including his parents, and then firing on motorists on Interstate 295, just days after being released from prison. Law enforcement officials released more information on Wednesady including identities of the victims of the shootings at a home in Bowdoin and 40km to the south on the highway in Yarmouth, Maine. Joseph Eaton, 34, had been released on Friday from the Maine Correctional Center in Windham, where he was picked up by his mother after completing a sentence for aggravated assault, police said. That crime was serious enough to prevent him from possessing a gun in Maine. The shootings in Maine began in the small town of Bowdoin, where four people were killed on Tuesday, with three bodies discovered in a home and one in a barn, police said. Then a chaotic scene developed in which shots were fired at vehicles on an interstate highway over 32 kilometres away in the community of Yarmouth, police said. Three people were shot there, and one remained in critical condition on Wednesday. The seven people shot on Tuesday were the latest victims of mass shootings in the US, whose targets included a Christian primary school in Nashville, Tennessee; a bank in Louisville, Kentucky, and a Sweet Sixteen party in a small city in Alabama. "This is an active investigation with a lot of moving parts," state police spokeswoman Shannon Moss said on Wednesday. The day before the shootings, an anguished man believed to be Eaton posted a roughly two-minute live video on Facebook criticising people who he said are Christian and do not give people a second chance. "What good does it do to hate somebody?" he said, choking back tears on the video. "You know, it destroys you." On the day he was released from prison, the man believed to be Eaton posted on Facebook that he was feeling thankful. "It's finally over. There are so many people I can't wait to see." Moss confirmed that state police were aware of the video, and that it is part of their investigation. Eaton, who was living in Bowdoin, was charged with four counts of murder but was not immediately charged in the highway shootings, she said. He was jailed while awaiting a court appearance. It was unclear if he had a lawyer to speak on his behalf, a jail official said on Wednesday. The names of the victims were not released, and state police didn't discuss any possible motive. Ian Halsey, of Bowdoinham, said that two cousins were shot and that his uncle suffered shrapnel injuries in a single car. One of his cousins is in critical condition and none of the family knew the shooter, he said. "They were just passersby in the wrong place at the wrong time," he said of his family. "It's horrible what happened." Eaton was charged over the past decade with more than a half-dozen crimes and served an eight-month sentence last year for assault, according to state records. Past convictions included aggravated assault, a felony that would prevent him from legally having a firearm. The origins and ownership of the firearms used in Tuesday's shootings were unclear. State police declined to comment on the weapon that was used. Australian Associated Press