Police hunting for the body of a 12-year-old boy killed by "Moors Murderer" Ian Brady in one of Britain's most notorious crimes said on Wednesday they had exhausted all leads and were suspending their search.

Lovers Brady and Myra Hindley were jailed for life in 1966 for a two-year reign of terror when they abducted, tortured and murdered five children, burying four of them in shallow graves on Saddleworth Moor near Manchester.

The bodies of two of the children were found on the moor in 1965 and that of 16-year-old Pauline Reade was discovered in 1987, but the remains of 12-year-old Keith Bennett, killed in 1964, have never been found.

Greater Manchester Police said their search for the boy's grave would remain suspended unless Brady agreed to helped them find its location or there was a fresh scientific breakthrough.

"Sadly we have not found his body and we reluctantly have to say that for now we have exhausted all of the avenues available to us," said Detective Chief Superintendent Steve Heywood.

He appealed to Brady to cooperate and allow the boy's mother Winnie give her son a proper funeral after 45 years.

"He's got one chance, if he's got any humanity left, to come forward and give us substantial information in relation to the grave," Heywood told BBC television.

Police went to see Brady at the high security Ashworth Hospital in 2003 when they reopened their search, but he refused to see them.

Since then officers have conducted periodic operations on the moor based on what Hindley had told them about where the body was buried, along with photographs taken by Brady at the time.

Scientists believed some of the boy's remains would be preserved, due to the nature of the moor soil.

The investigation had involved clinical psychologists, imagery experts, geologists, geophysicists, geochemists, archaeologists and anthropologists.

The sadistic nature of the killings made Brady and Hindley among the most despised figures in Britain.

During their trial, the court heard tape recordings made by the couple of their victims pleading for mercy before they were tortured and killed.

Hindley was Britain's longest serving female prisoner when she died in 2002 after 36 years in jail.

"I am 76 in September and I just want Keith found," the boy's mother, Winnie Johnson said in a statement.

"I will never give up as long as I have breath in my body -- not just for me but for my family and all of those around me."