The BBC's Philippa Thomas in Washington: "Dr Kevorkian says he is prepared to die in jail"

Investigators decided to take action after viewing a video recording made by Doctor Jack Kevorkian as he injected 52-year-old Thomas Youk with lethal drugs.

Edited parts of the recording were broadcast on Sunday on CBS's popular news show, 60 Minutes.

Dr Kevorkian - a 70-year-old retired pathologist known popularly as 'Dr Death' - has been arraigned and released on bail after turning himself in.

He has said he wants to provoke a legal showdown over assisted suicide and euthanasia.

Thomas Youk asked Dr Kevorkian to administer a lethal injection

Mr Youk, who was suffering from an irreversible wasting illness, Lou Gehrig's disease, had given written consent for a lethal injection to be administered and agreed for his death to be videotaped.

But prosecutor David Gorcyca said: "Consent is not a defence in the state of Michigan."

Dr Kevorkian has been tried and acquitted in three previous trials involving five deaths.

He has acknowledged a role in some 130 assisted suicides since 1990, but Mr Youk's death was the first time he directly administered the lethal dose of drugs.

'Based on law not sympathy'

In addition to murder, Dr Kevorkian is being charged with criminal assistance of a suicide and delivery of a controlled substance.

Oakland County prosecutor David Gorcyca: Decision based on law

"It is incumbent upon me to make charging decisions based solely on the law and not emotion or sympathy," Mr Gorcyca said.

BBC Washington Correspondent Nick Bryant says Mr Gorcyca was elected to his post two years ago, in part because he said he would not put Dr Kevorkian on trial until state legislators devised a clear law on doctor-assisted suicide.

Since then a law has been passed making assisted suicide a felony punishable by five years in prison or a $10,000 fine.

The charge of first-degree premeditated murder is much more severe - mandatory life in prison.

Dr Kevorkian has said previously that if he is convicted and jailed he will go on hunger strike.

He has said he will represent himself in any trial, but will be advised by university law professor Robert Sedler.

Two drugs

The footage screened on CBS's 60 Minutes showed Mr Youk, of Detroit, Michigan, twice signing a consent form after Dr Kevorkian asked whether he wanted the lethal injection to go ahead.

Viewers saw Dr Kevorkian administering two drugs, one to make the patient sleep and one to stop his heart.

In the broadcast, reporter Mike Wallace asked Dr Kevorkian: "You killed him?"

The doctor replied: "I did, but it could be manslaughter not murder.

"It doesn't bother me what you call it. I know what it is."

Some of Mr Youk's family took part in the 60 Minutes programme. His wife Melody said: "I was so grateful to know that someone would relieve him of his suffering.