Jack Kevorkian, the man known as Dr Death and who helped the terminally ill to die, has been released from prison in the US state of Michigan.
Jack Kevorkian: Controversial and divisive figure
Kevorkian was convicted in 1999 of the murder by injection of terminally ill Thomas Youk. A video of him dying was broadcast on television.
Kevorkian, 79, had served eight years of a 10-25 year sentence.
He has pledged not to counsel people on suicide but says he will continue to fight for the right to euthanasia.
Kevorkian won parole after an appeal based on his own failing health.
He emerged from prison, with his lawyer and a correspondent for the CBS television network, saying the release was "one of the high points of life", the Associated Press news agency reported.
The BBC's Jeremy Cooke in New York says Jack Kevorkian was among the most controversial and divisive figures in 1990s America.
The elderly former pathologist insisted that patients living in pain had the right to die.
Our correspondent says Kevorkian proudly claimed to have helped some 130 people to end their lives, many using his so-called mercy machine, which delivered lethal amounts of drugs intravenously.
Some of the assisted suicides were in the back of his Volkswagen van.
His methods alienated many. In 1998 he offered on a "first come, first served" basis the kidneys of a man he had helped to die.
Thomas Youk's death was shown on national television
Kevorkian fought a long battle with the authorities in Michigan, thwarting four attempts to convict him despite the revocation of his medical licence in 1991 and a ban on assisted suicides to stop his work.
Thomas Youk suffered from ALS, or Lou Gehrig's disease, a wasting disorder of the nervous system, also known as motor neurone disease.
A jury convicted Kevorkian of second-degree murder after watching the video of him injecting lethal drugs into Mr Youk.
Kevorkian had sent the video for broadcast on the CBS show 60 Minutes.
He plans to return to the show in an interview on Sunday.
Prior to his release, Kevorkian told a TV station in Detroit: "[Euthanasia] has got to be legalised. I'll work to have it legalised but I sure won't break any laws."
Jack Kevorkian with his "mercy machine" in 1991
His release coincides with a key vote next week in California on allowing assisted suicides. Only the state of Oregon has passed such legislation.
Kevorkian's release has brought mixed emotions from the relatives of those he helped die.
Thomas Youk's brother, Terry, said: "It was a medical service that was requested and... compassionately provided by Jack. It should not be a crime."
But Tina Allerellie believed her sister, Karen Shoffstall, was suffering depression and doubted that she wanted to die.
"His intent, I believe, has always been to gain notoriety," Ms Allerellie said.