SAINT JOHN, N.B. -- A forensic expert says he cannot tell how old the bloodstains are on the jacket Dennis Oland was wearing the day his father was beaten to death, or how they got there.

The brown Hugo Boss jacket is key prosecution evidence at the Oland murder trial.

It has the only blood evidence potentially linking Dennis Oland to the scene where his father, Richard Oland, was killed in 2011.

But RCMP Sgt. Brian Wentzell, a forensic bloodstain expert, told the trial Friday he has no way of knowing how four small bloodstains from Richard Oland got on the jacket or how long they were there.

Oland had the jacket drycleaned in the days following his father's murder.

Defence lawyer Alan Gold said during his aggressive cross-examination of Wentzell that it is possible the bloodstains could be the result of "innocent transfer," referring to something like a nosebleed or a small cut.

"You cannot say how those stains got on the jacket can you?" asked Gold.

"No," answered Wentzell.

"You can't say it was spatter and you can't say how old they are, can you?" Gold asked.

"No," the bloodstain expert said.

Dennis Oland, 51, told police on July 7, 2011, the day his father's body was found on the floor of his Saint John office, that he was wearing a navy jacket when he visited his dad late on the afternoon of the previous day.

But eyewitness accounts and security video showed he was wearing the brown jacket that was later found to have the four small bloodstains on its exterior.

The trial already has heard from several witnesses that multimillionaire businessman Richard Oland liked to touch people when greeting and talking to them.

"There is nothing inconsistent with them being innocent transfer," Gold asked Friday, referring to the bloodstains on the jacket.

"No," Wentzell answered.

Despite blood spatter that radiated in all directions during the killing on July 6, 2011, no blood was detected in the car Dennis Oland was driving that day, on items he was carrying, such as his cellphone, or on his clothing - except for the jacket.

Wentzell said he, like other police officers involved in the case, did expect the assailant who killed Richard Oland would have blood spatter on their clothing.

But in the case of Dennis Oland, it is largely absent - apart from the four tiny stains on the jacket that are almost impossible to see with the naked eye.

"It's a reasonable inference - there is no way that jacket was worn during the blood-letting?" Gold asked Wentzell.

The question prompted an objection from Crown prosecutor P.J. Veniot, and Wentzell did not answer.

The bloodstain expert explored the tale told by the patterns of blood at the crime scene during his testimony for the prosecution on Thursday. Richard Oland, 69, at the time of his death, was killed by more than 40 blows to his head that cracked his skull and sent blood, bone and brain matter flying around the room.

But Wentzell said the amount of blood and gore that lands on an attacker is impossible to calculate. It depends, he said, on the angle of the blows and the type of weapons used.

Oland was struck with a blunt, hammer-like object and a sharp-edged implement. The weapon was never found but some have suggested it could have been a drywall hammer that has both a hammer and an axe side.

"I am aware of a case where a person was stabbed multiple times in a vehicle, and there was no blood found in the vehicle," Wentzell said.

Friday was day 35 of Oland's retrial for second-degree murder. He was charged with the killing in 2013 and convicted in a jury trial in 2015. However, the verdict was overturned on appeal in 2016, due to an error in the judge's charge to the jury, and the new trial was ordered.

The current trial, before judge alone, is expected to conclude by mid-March. The judge is then expected to take at least two months to render a verdict.