Adrian Palmer's body was found in an alleyway
An inquiry into the killing of a man who had complained about receiving threatening messages has found police responsible for a number of "failings".
The body of Adrian Palmer, 21, was discovered in an alleyway in Tenbury Wells, Worcestershire, in May 2006.
A 23-year-old man from Tenbury Wells was convicted of Mr Palmer's manslaughter in December 2007.
The police watchdog said the inquiry substantiated misconduct against two West Mercia officers.
The investigation by the Independent Police Complaints Commission found an allegation of male rape made by Mr Palmer, who had Asperger's Syndrome, should have been investigated more thoroughly.
It also found police failed to look properly into threatening messages made to Mr Palmer's mobile phone weeks before his death.
An IPCC spokesman said the inquiry substantiated allegations of misconduct against two officers for failing to ensure a thorough criminal inquiry was undertaken.
Commissioner Len Jackson said Mr Palmer deserved to have his allegation dealt with more seriously.
West Mercia Police said all the IPCC recommendations had been accepted and implemented.
'Words of advice'
Deputy Chief Constable David Shaw said: "A great deal of work has already been done to improve the way that victims of sexual assault are dealt with by this force.
"We want to reassure our communities that complaints of rape are taken extremely seriously by West Mercia Police.
"We voluntarily referred this matter to the IPCC and we welcome the chance to improve working practices even further now the scrutiny of the IPCC investigation is completed.
"As recently as last week the force hosted a rape seminar at police headquarters which was a good opportunity for our officers and staff to gain further knowledge.
"We also work with other agencies to promote awareness of issues such as autism so we can better help those vulnerable members of society such as Adrian.
"We note that the IPCC cannot say that the actions by West Mercia Police officers ultimately contributed to Adrian Palmer's death."
He said the two officers mentioned would be issued "with words of advice".