Media playback is unsupported on your device Media caption The film shows James Earl Ray being marched into a jail cell and later strip searched

Long-lost video showing Martin Luther King's killer in police custody has been posted online, 45 years to the day after the civil rights leader's murder.

Officials in Tennessee unearthed the tapes of James Earl Ray in 2011 but had no way to view the old technology.

Ray is seen in 1968 on a plane after extradition from Britain and as he is searched and given a medical exam and a bulletproof vest at a Memphis jail.

King, a Baptist minister, was shot in Memphis on 4 April 1968, at age 39.

Ray, a racist drifter and bungling career criminal, was captured in London by Scotland Yard detectives two months later.

Extradited to Memphis, he avoided a jury trial - and possibly the electric chair - by entering a guilty plea the following year.

He was sentenced to 99 years in prison. He later recanted his confession, saying he had been framed by shadowy conspirators, but his guilty plea was repeatedly upheld in the courts. He died in 1998 at 70.

The footage of Ray in custody was discovered in the Shelby County sheriff's office along with logs and photographs from the investigation.

Mistrial fears

County officials had seen a photograph taken during the investigation of an employee from that time showing a video.

Image caption Martin Luther King's assassination provoked a national outpouring of grief as well as riots in some major cities

And Harvey Kennedy, a former sheriff's department employee, told staff of a box of Ray materials in his old office.

Researchers found the tapes, which were in an early video format that could not be played in Shelby County, so they sent the tapes to New York for conversion into current technology.

"It's kind of like Christmas when you get these tapes, but then you can't play them back," Tom Leatherwood, the county's register of deeds, told the BBC.

Researchers now say Shelby County authorities bought the cameras and planned to film Ray's arrest and trial to prevent any chance of mistrial, should his defence claim police mishandled the investigation or the procedure.

"We have the invoices and owner's manual of the equipment," Mr Leatherwood said. "It was purchased specifically because they were about to take James Earl Ray into custody."

The footage shows Ray being read his Miranda rights, which are guarantees under the US Constitution of fair treatment during questioning, by Sheriff Bill Morris.

Image caption Before his arrest for the murder, Ray had been a bumbling career criminal

The tapes also show police outfitting Ray in a bulletproof vest to ensure that unlike John F Kennedy's assassin Lee Harvey Oswald, he would make it to trial alive.

"No law enforcement agency wanted that to happen under their jurisdiction," Mr Leatherwood said.

Though Ray never stood trial, county officials filmed inside the courtroom during initial proceedings.

After researching security procedures from the trial of Robert F Kennedy's assassin Sirhan Sirhan, county officials asked everyone who entered the courtroom, including would-be jurors, to identify themselves on tape.

The jurors were all male, and only two were black.