“This day is the end of a long journey and a dream realised,” she told the TT news agency.
For the past year, Östberg has been held in a rehabilitation centre in Basta, south of Stockholm. She has been working at a day nursery for dogs as part of the preparations for her release.
Östberg spent 28 years imprisoned in the US after being convicted in 1983 for her role in two murders.
She was transferred to Hinseberg prison, near Örebro in central Sweden from a California jail in the spring of 2009.
In October 2009 she was moved to Färingsö prison in eastern Sweden, a lower security facility.
In November 2009, the district court in Örebro reduced her life sentence to 45 years, ruling that there was no major risk she would revert to violent crime.
Under Swedish law, convicted criminals are eligible for release after serving two-thirds of their sentence. In Östberg’s case, this corresponded to a May 2011 release and that timetable has now been kept.
Östberg had difficulty explaining her feelings on becoming a free woman, saying that she has felt free since returning to Sweden.
“The same second that I set foot on Swedish soil I felt free, and especially when I came to Basta,” she said.
She told TT that it felt nice not to have to be monitored by the Swedish Prison and Probation Service (Kriminalvården) and said that she planned to celebrate with a cake.
“I have been given a Princess Cake which is my favourite. I am going to go out into the woods and then some friends are coming to visit,” she said.
Östberg moved to California with her mother in the 1960s. Having suffered from serious drug problems she later started a relationship with a drug dealer, Brian Cox.
In April 1981, Cox, accompanied by Östberg, shot dead two people in separate incidents.
Cox hanged himself in his cell prior to the trial, while Östberg was convicted and sentenced to life in prison for the murders.