Ex-cop questions Claremont murder case

A retired police officer has questioned the comprehensiveness of investigations into Perth's most notorious set of unsolved murders.

Former West Australian officer Con Bayens says police looking for the Claremont serial killer in the 1990s and 2000s were dismissive of a suspect because they were too focused on trying to tie another man to the crime.

Mr Bayens told the Seven Network he pulled over a man who he believed was a suspect during an undercover operation in Highgate many years ago.

"What I saw that night has haunted me for a lot of years," he said on Sunday.

The boot was lined with blue plastic and there was a pair of pliers and masking tape.

The driver was questioned but Mr Bayens does not know why he was cleared in inquiries by officers on Task Force Macro, which was set up to investigate the killings.

Mr Bayens said the head investigator into the killings had rejected his offer to pass on information from the undercover operation.

"He said, 'Don't worry about it, Con, we've got our man.' And those words will stick with me forever," he said.

"That just hit about 10 on my weird shit-o-meter."

Police are still hunting for the killer of Jane Rimmer, 23, Ciara Glennon, 27, and Sarah Spiers, 18, who were abducted and murdered after partying at nightspots in the affluent suburb of Claremont.

The case is Australia's longest-running and most expensive murder investigation.