A relative said she plans to visit Oregon, where she lived quietly under an alias for years, but did not say when.
The 50-year-old woman said nothing to reporters as she left MCI-Framingham, where she had spent six years. Two unidentified women escorted her into a car and drove off.
But in a statement issued by her lawyer, James M. Doyle, Power said she "will always carry my human responsibility" for her role in the death of Officer Walter Schroeder, a father of nine.
"This is a time to acknowledge that a human life, once lost, is lost forever: that the death of a father, husband, and brother is a terrible event, and one for which I will always be deeply sorry," Power's statement said.
Power was a 21-year-old student at Brandeis University in 1970 when she and four fellow activists robbed a bank in Boston's Brighton neighborhood to fund efforts against the Vietnam War. She was waiting in the getaway car when William "Lefty" Gilday shot Schroeder in the back.
Only Power got away. Gilday was convicted of murder and sentenced to life in prison.
Power took the alias Alice Metzinger, lived in women's communes, gave birth to a son and settled in Lebanon, Ore., where she married a bookkeeper, Ronley Duncan, and became known for her cooking at a tea and coffee house.
After beginning therapy for depression, she returned to Massachusetts in 1993. She pleaded guilty to manslaughter and was sentenced to eight to 12 years.
She was released early with credit for good behavior and time served.
Power's release comes as another radical who spent years as a fugitive, Sara Jane Olson, formerly known as Kathleen Ann Soliah, awaits trial on charges that she planted bombs under Los Angeles police cars in 1975 as part of a conspiracy by the Symbionese Liberation Army. She was arrested in June in St. Paul, Minn., where she had settled into a comfortable life as an actress, a doctor's wife and a mother of three.
In Power's case, Schroeder's family maintains that she has been punished too lightly. "I think six years is a fairly light sentence when you're talking about circumstances involving the death of somebody," daughter Clare Schroeder said recently.
Although Power hasn't said where she will go next, her brother-in-law, John Whittaker of Denver, said her plans include trips to Colorado and Oregon.
"But other than that, we have no idea what her future plans are," he said in a telephone interview Saturday. "We're all looking forward to uniting with her when she gets to Denver."
Power and Duncan are still legally married, but he has said he hasn't spoken with her in the past year. Last week, Duncan said he didn't even know she was to b released.
In Oregon, people who knew Power as Alice Metzinger have largely taken a forgiving attitude.
"She was a good citizen when she lived here and I expect she will be when she comes back," said police Detective Sgt. John Atchley. "She was so quiet when she lived here that a lot of people don't really know who she is."