British police are re-examining 58 unexplained deaths following the conviction of a date-rape serial killer.

A judge sentenced Stephen Port, 41, to life imprisonment for the murder of four young gay men he met through online dating platforms such as Grindr.

The chef was also convicted of 18 other offenses, including four rapes and four sex assaults against other men. He has no possibility to request parole. 

He slipped fatal doses of the drug GHB into his victims' drinks, raped them while they were unconscious, and then dumped their bodies at a local cemetery.

But the case has revealed gross inadequacies in the police response to the deaths. It was only the pleas of the final victim's family that spurred police to investigate the deaths as potential homicides.

The UK's independent police watchdog is now investigating why police initially failed to link the four deaths. All the victims were between 21 and 25, and their bodies were all found near Port's east London home over a 15-month period. Two of them were found propped up against gravestones by the same woman walking her dog.

Human rights campaigner Peter Tatchell accused the police of letting Port "slip through their fingers". He said friends of two of the victims felt "fobbed off" when they voiced their concerns to police. "To have three young men found dead in public places in mysterious, unexplained circumstances - all within a few hundred yards of each other and within the space of three months - should have triggered alarm bells," Tatchell said. "If four young middle class women had been murdered in Mayfair, I believe the police would have made a public appeal much sooner and mounted a far more comprehensive investigation.

Police are now investigating 58 unexplained and GHB-related deaths over the past four years in London. Judge Peter Openshaw said Port should die in prison for his "dreadful offenses."

One of the victims' sisters said they have finally received justice. "A sick and twisted scumbag will never be able to hurt or destroy any other family's life," Jack Taylor's sister Donna said outside court.

aw/kl (dpa, Reuters, AP)