Two days after a Dunedin woman was found dead outside her workplace last December, the blood-soaked hammer allegedly used to bludgeon her was found in a bin outside a colleague's home.

Alexander James William Merritt (21), is on trial in the Dunedin High Court charged with the murder of 51-year-old Karin Ann Ross.

The victim - his supervisor at Spotless Cleaning Services - was found face down in a pool of her own blood by the defendant's mother Sharon in the business's Strathallan St car park in the early hours of December 2 last year.

Merritt had finished his shift about five hours earlier and told police in an interview on December 4 that he went straight home and did not leave the house until the next day.


But while officers spoke to the cleaner, a specialist search team was scouring the Merritt family's Kaikorai home.

Crown prosecutor Richard Smith said inside the house they found blood on a bathroom cold tap and on cabinets.

Outside the Nairn Rd address in a wheelie bin it is alleged police found a blood-soaked hammer and a glove wrapped in a heavily-bloodied top.

Smith told the jury in his opening address yesterday that DNA testing of some of the samples showed the blood was one million million times more likely to be Ross's than anyone else's.

During the interview, officers also quizzed Merritt about "obvious" scratches on his face.

"He said he had scratched himself in his sleep," Smith said.

But the prosecutor told the jury they should reach a different conclusion.

"You can infer they were made by Karin Ross as she fought for her life."

Smith said there was evidence the victim had struggled with her attacker and attempted to escape.

Ross had 32 separate bruises to her hands and arms to go with the 14 injuries to her head, which the Crown called "dramatic and extensive".

When police arrived at the scene they found the victim's white van had collided with a skip.

There was blood inside the vehicle and a bloody handprint on the outside, Smith said.

The Crown said no motive had to be proven but in this case Merritt had made his hatred of the victim clear.

"I would like to burn her family in front of her," he allegedly told one colleague.

"That lazy b****. It would be fine if she died," the Crown said he told another.

Ms Ross had recently cut the defendant's hours at the business and days before the alleged murder Merritt had been informed of disciplinary proceedings being initiated against him.

He had continually parked in a disability spot and was censured for his behaviour around other staff, the court heard.

The day before he allegedly attacked Ms Ross, he received a statement from her and another staffer in which they outlined their concerns about his conduct.

Defence lawyer Anne Stevens said raising the comments her client allegedly made served no purpose but to "blacken his character".

"Most of us have been guilty, I suggest, of making similar comments in times of anger and frustration; particularly in a work situation," she said.

The lawyer was also critical of evidence that would be heard about cellphone tower data placing Merritt away from his home at 1.34am - the approximate time of Ms Ross's death.

DNA findings would be rigorously challenged too.

"The scientific evidence the Crown places so much reliance on has inherent uncertainties,"Mrs Stevens said. "There are surprising gaps in that evidence."

The trial before Justice Nicholas Davidson and a jury of four women and eight men is scheduled to last two weeks.