Child welfare investigators described in 1984 how Seattle Mayor Ed Murray repeatedly raped his teenage foster son, three decades before the allegations became public.

Jeff Simpson, 49, is one of four men who say Murray, now 62, abused them when they were teenagers.

Former crack addict Delvonn Heckard was the first to have his allegations reported in April this year. Two other former addicts - Lavon Jones and Lloyd Anderson - also say they were abused.

Murray has always denied the allegations and has never been prosecuted.

On Sunday, The Seattle Times published a newly unsealed report that was written in 1984 by child welfare officials. The report was prompted by claims made by Simpson at the time that he was being abused and it concluded that Murray was guilty of the accusations.

Child welfare investigators found in 1984 that Seattle mayor Ed Murray (left in May) sexually abused Jeff Simpson (right) when the latter was a teenager and living in Murray's care

The report was finally unsealed this month by authorities in Oregon which had previously kept it hidden

'In the professional judgement of this caseworker who has interviewed numerous children of all ages and of all levels of emotional disturbance regarding sexual abuse, Jeff Simpson has been sexually abused by Edward Murray,' Child Protective Services caseworker Judy Butler wrote.

She added that 'under no circumstances' should Murray be allowed to care for any other minors.

Prosecutors investigated Murray at the time but chose not to bring charges against him because of Simpson's troubled personality.

'It was Jeff's emotional instability, history of manipulative behavior and the fact that he has again run away and made himself unavailable that forced my decision,' Deputy District Attorney Mary Tomlinson wrote.

She added: 'We could not be sure of meeting the high burden of proof in a criminal case - of proof beyond a reasonable doubt and to a moral certainty. However, this in no way means that the District Attorney's Office has decided Jeff's allegations are not true.'

Devlonn Heckard sued Murray in April, claiming he too had been abused as a drug-addicted teenager

The report was made public at the request of the Seattle newspaper which demanded that Oregon's Department of Human Services unseal the report findings earlier this year.

The agency withheld the documents for years but finally agreed this month that it was in the public interest to release them.

Dismissing the report on Sunday, Murray said he was never interviewed as part of the child welfare investigation. He reiterated that he had never been prosecuted.

'That she believed Jeff's claims at the time and advocated on his behalf is painful to see, but does not change the fact that, based on the totality of the evidence that was collected, the District Attorney declined to file charges,' he said of the child welfare investigator's findings.

Simpson, now 49, had been abandoned as an infant. He lived under Murray's care for nearly a year and a half as a teenager, after meeting him when Murray counseled him at a Portland center for troubled teens in the late 1970s.

Simpson said the abuse began in 1980, when he was 13 and spending a weekend with Murray. The abuse continued after Murray became his foster father and lasted until he left Murray's care at age 16, Simpson said. At times, Murray paid Simpson $10 or gave him drugs for sex, he said.

The men say they got to know Murray while frequenting this center for troubled teenagers in Seattle in the 1980s, long before the mayor launched his political career

Murray (pictured in April this year at a press conference after the first allegations were made) has always denied the men's claims

He considered suing Murray in 2008, but his lawyer declined to pursue the case over a statute of limitations issue. By then, Murray was a Washington state senator, Democratic powerbroker and gay rights advocate. He was elected mayor in 2013.

Simpson added that he and his attorney had tried to find such documents, but they were told none existed.

Heckard, the other man who claims he was abused, sued Murray in April this year.

His allegations were similar to those made by Simpson and center around claims the politician picked him up in the streets and paid him for sex in cash or drugs.

Murray denied his claims immediately, insisting the pair never had any form of sexual relationship.

Heckard withdrew his lawsuit last month. His lawyer said the decision was based on his desire to complete counseling and the fact that Murray is still sitting as Mayor of Seattle.

After the initial allegations in April, Murray halted his campaign for re-election. He will serve as the city's mayor until November this year.