Three police investigations involving a man who was tortured and killed before his headless body was dumped in a lake were "flawed", the Independent Police Complaints Commission (IPCC) has said.
Michael Gilbert, 26, was kept as a slave and tortured for his benefit money before being killed. His decapitated body was dumped in the Blue Lagoon in Arlesey, Bedfordshire, in 2009.
Last year, three members of the Watt family were jailed for life for murder, and three others for familial homicide, as a judge branded their crime "depraved".
The IPCC said a Serious Case Review had looked at the consequences of actions by police and other agencies who had contact with Mr Gilbert, but the watchdog has investigated police handling of incidents involving Mr Gilbert before his murder.
The probe comes after Mr Gilbert's mother contacted the body in July 2010, alleging police had failed to investigate three incidents involving her son. These were an assault in Luton in 2002 and abductions in Cambridgeshire in 2007 and in Lancashire in 2008.
On Thursday, the IPCC said police had investigated each of the incidents, but all three inquiries were inadvertently hindered.
The 2002 assault investigation was hampered after it was given inaccurate information from other public services; the Cambridgeshire abduction inquiry was not told Mr Gilbert confirmed to a Bedfordshire officer that he had been taken against his will, having previously denied it.
And in Lancashire, the wrong mobile phone number was written down for Mr Gilbert, the IPCC said.
Commissioner Rachel Cerfontyne said: "This is a tragic case and one where the horrific manner of Michael's death must make it even harder for his loved ones to cope with their loss.
"We looked at specific allegations that the police did not investigate three incidents involving Michael and the Watt family. We have found that on each occasion investigations had taken place, but were flawed due to misinformation, failures in communication and human error."