A man wanted in the United States for the murders of two Mormon missionaries has died in London while awaiting extradition.
Kleasen maintained his innocence
Wheelchair-bound Robert Kleasen, 70, died of suspected heart failure in a London hospital on Monday.
He was wanted in the US for a retrial for the murders - 29 years ago - of Mark Fischer and Gary Darley.
Kleasen was, until recently, being held in custody at Belmarsh prison in south London.
He was transferred to the Queen Elizabeth Hospital in Woolwich on 17 April, where he died.
A Prison Service spokesman said on Monday: "He died this morning at 6.15am of suspected heart failure.
"Whether there is a post mortem is a matter for the coroner.
"His next of kin have been informed."
Kleasen was found guilty of the murder of 19-year-old Mark Fischer.
He spent two-and-a-half years on death row in Texas before his conviction was quashed.
But last summer, a judge at Bow Street Magistrates' Court in London agreed to a request by the US government that Kleasen be sent back to Texas to stand trial for the double murder.
Mr Darley, 20, and Mr Fischer were killed on 28 October, 1974 in Travis County in Texas.
The decision had to be approved by the home secretary and was subject to an agreement by the US authorities he would not be executed.
He moved to the UK in 1990 and married pen pal Marie Longley, from Barton-upon-Humber, near Scunthorpe, after serving a sentence for federal firearms violations.
But fresh DNA evidence linked him to the scene
of the crime and the US government sought an extradition.
The two missionaries were from the Church of Jesus Christ of the Latter-Day Saints - the Mormons.
US prosecutors said they disappeared after going to his trailer when he asked them over to eat venison.
It was alleged Kleasen harboured a grudge against the Mormon church because he felt it had neglected him when he was in jail for buffalo poaching.
A band saw found in a taxidermist's shop the next day had human tissue and hair on its blade, later shown to belong to the victim.
A prayer book, watches and keys belonging to the victims were found near Kleasen's trailer.
But he was originally acquitted on appeal in 1977 because of an illegal search warrant.
Then advances in forensic science prompted the Texas authorities to re-examine the murders.
Last August, when Judge Workman decided there was a case to answer, he said DNA tests conducted in 2000 revealed an "overwhelming probability" that blood found on clothes near Dr Kleasen's trailer was Mr Darley's.
In June 2000 he was sentenced to three years imprisonment at Grimsby Crown Court for illegal firearms possession.
Kleasen, who frequently claimed to be a doctor despite the lack of any proper qualifications, was arrested as he left Rye Hill prison near Rugby, Warwickshire, in October 2001.