Expert explains how murder suspect’s DNA could have gotten on Sweeney’s fingernails

A forensic biologist with the Centre of Forensic Sciences testified Friday that physical contact is the most likely way that Robert Steven Wright’s DNA was found on Renee Sweeney’s fingernails.

However, Renata Dziak said that casual contact can’t be ruled out as the source of the DNA. She also said her conclusions do not imply anything about the nature of the physical contact.

“Some degree of force does not imply violence,” Dziak said.

“It just implies … there was direct contact with some degree of force.”

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Dziak was testifying at Wright’s second-degree murder trial, which is in its third week in Sudbury. Sweeney was stabbed to death Jan. 27, 1998, while she was working as a part-time clerk at Adults Only Video on Paris Street.

Wright was charged in December 2018 and officials said at the time that DNA evidence was key in making the arrest.

On Friday, Dziak said she reached her conclusions using DNA recovered from Sweeney’s nails, as well as “debris” that was found in the jar containing the fingernails from her right hand.

The best DNA sample was in the debris, she said.

But she said even if she was only relying on scrapings from the actual nail, “my opinion would be the same.”

Crown prosecutor Rob Parsons asked whether it was equally possible that the DNA was transferred when someone was trying to help Sweeney or when someone was attacking her.

“One of those scenarios is not more likely than the other,” Dziak said.

“I can’t tell you one is more likely than the other.”

DNA CAN TRAVEL

She explained different ways that someone’s DNA could end up on someone else.

Direct contact is the most obvious way, but she said indirect transfers can happen, too. For example, if you cut your finger and the blood drips on the floor, someone walking on that floor could get a blood stain on their sock.

And the stain on the sock could end up on a bathroom floor.

“In that case, there was no direct contact,” Dziak said, but the transfer still occurred.

DNA also can be transferred either through bodily fluids or from “shedding” of things like dead skin cells, she said.

You can get someone else’s DNA on you in a number of indirect ways, she said. For example, if you live in the same house or share an office space.

Defence attorney Michael Lacy asked her what she knew about how Sweeney’s fingernail clippings were collected and stored to prevent contamination.

“You’re assuming the samples were not contaminated, correct?” Lacy asked.

“I’m not assuming anything,” she replied. “It’s an unknown for me whether contamination would have happened.”

“I’m just looking at the presence of the DNA in that sample. I can’t speak to anything that happened to the fingernails before they got to the laboratory.”

Lacy asked her whether the presence of Wright’s DNA excludes the possibility that someone else was responsible for Sweeny’s death.

EVERYONE SHEDS DNA

No, she responded, and said you don’t necessarily leave DNA when there is contact with someone else -- even with “some degree of force.”

Dziak said how much a person sheds varies person to person. Even people will shed DNA at different rates depending on the circumstances.

She also agreed that the DNA evidence tells her nothing directly about the identity of the perpetrator in this case. It could have been left on the fingernails under a number of different situations that were not violent.

“It’s not more likely than any other scenario,” Dziak said.

The Crown didn’t formally finish its case Friday morning, but is expected to wrap up Monday.

Wright is expected to testify in his own defence starting as early as Monday afternoon or Tuesday. 

The trial resumes Monday morning. CTV News digital content producer Darren MacDonald and videojournalist Ian Campbell will be in the courtroom all day Monday and will have updates on CTVNewsNorthernOntario.ca.