SEVENTEEN minutes into the crime scene video, the blue tarpaulin is clearly visible.

Laid out behind a shed with two tyres holding it down, no-one knows what's under it - because no-one has looked.

All day, since just after 10am on the morning of February 26, 2010, police and forensic examiners have walked past this blue plastic cover in Scott St, Greenmount, in Perth's hills district.

But only one person at that time knows the secret it hides - the killer of the woman whose bludgeoned body lies beneath it.

The body belonged to Sidney de Beaux, 35, and police believe her killer is the same person who killed Stefan Borsa, 64, whose brutally bashed body was found in her house 12 hours earlier.

Today, Andrei Peter Hedgeland, 36, appeared for the second day of his trial in the Perth Supreme Court, charged with their murders.

He admits to being at Ms de Beaux's house on the night of the alleged crimes, but says he did not kill the pair.

He and Ms de Beaux were friends and fellow heroin users, the court has been told.

She was a small-time drug dealer, Hedgeland a "wannabe".

Mr Borsa was their heroin supplier, the court has heard.

Police witnesses told the court today they were so involved in the initial investigation into Mr Borsa's death that they failed to find Ms de Beaux's body lying behind the shed.

Possibly a dozen officers had walked straight past it.

This was despite being sent to her house earlier in the morning to look for her, after she was reported missing.

Instead, they found the bloodied body of Mr Borsa lying on her couch, a hydroponic cannabis plant near the bedroom, a burned out car, and a house full of gas in an apparent attempt to blow it up.

Not until after 10pm that night did two officers guarding the scene smell something behind the shed and find Ms de Beaux's body.

Senior Constable Graham Webster, one of the first officers on the scene, told the court he walked past the tarpaulin "two or three times" without looking under it.

There was already one apparent murder at the scene. No one thought there would be two.

In fact, Ms de Beaux was considered a prime suspect in the alleged killing of Mr Borsa.

"She was considered a person of interest, as she wasn't at the house," Detective Senior Constable Simon Sustek), who was briefly in charge of the crime scene, testified.

"We didn't believe (Ms de Beaux) was on the property," he said.

Even the forensic officer who videoed the scene walked straight past the body several times.

"I didn't know at the time (the body was under there)," Senior Constable Darryl Khng (Khng) testified when it was pointed out the tarpaulin could be clearly seen in his video.

Prosecutor Amanda Forrester alleges Hedgeland bludgeoned Mr Borsa and Ms De Beaux to death after a drug deal went bad.

Defence lawyer Linda Black said Hedgeland and Ms De Beaux were "good friends" and that there may have been two killers.

The trial is continuing before Justice Stephen Hall.