Forensic scientist says likely 'some degree of force' led to DNA left under Sweeney's fingernails

Earlier this year, Renata Dziak says she was requested to give her scientific opinion about the male DNA found under Renée Sweeney's fingernails. 

Dziak is a forensic scientist with the Centre of Forensic Sciences. She testified on Friday morning, at the Sweeney murder trial in Sudbury. 

43-year-old Steven Wright is standing trial for second-degree murder. He's accused of stabbing Sweeney to death, when he was a high school student, in 1998. 

Dziak told the court she evaluated different scenarios that could explain how the male DNA could have been transferred to the 23-year-old's fingernails — a key piece of evidence in the case.

She examined the DNA results taken so far, since 1998 when the murder first happened, and looked at how much DNA was present on the fingernails, as well as, "the quality" of that DNA.

2 scenarios

While on the stand, Crown attorney Robert Parsons asked Dziak to consider two scenarios. 

One was the male DNA associated with Sweeney's fingernails was left behind through close physical contact, which could include direct and indirect contact with the fingernails. 

An example of indirect contact, offered by Diziak earlier, was someone cutting themselves in the kitchen and their child stepping in the droplets of blood produced from the wound. While the child did not touch the wound, Dziak said, blood was still transferred onto the child's sock. 

The other scenario he asked Dziak to think about was the male DNA was transferred to Sweeney's fingernails through everyday casual contact, which could involve things like working in the same environment with someone or hugging a family member.

'Some degree of force'

Dziak told the court that based on the quantity of the male DNA found in Sweeney's fingernails, it was more likely there was direct contact, which included "some degree of force," than the DNA was transferred through casual, everyday contact between Sweeney and the person who left the DNA. 

She said that doesn't mean casual contact can be ruled out as a possibility but it was her opinion it was more likely that "some degree of force" through direct contact led to the DNA transfer. 

Dziak also clarified, "Some degree of force does not imply violence."

Parsons asked her if the degree of force, which led to the DNA transfer could be consistent with someone offering medical assistance. Dziak told the court it couldn't be ruled out. 

The majority of the population does not have foreign DNA under their fingernails, just walking around.— Renata Dziak, forensic scientist 

However, when asked if the degree of force leading to the DNA transfer could be consistent with someone fighting someone, Dziak said it's also a possible explanation.  

She also told the jury that in addition to peer-reviewed articles, she used her own research, conducted on DNA transfers to form her opinion.

Her study used 106 subjects who submitted samples of their fingernails, in order to see in what scenarios DNA would be left behind from people who weren't the owners of the fingernails — as well as, how much DNA was left behind.

She said the majority of the samples did not have any DNA left behind or a very low level was left behind and couldn't be compared for testing. 

Dziak pointed out that blood is one of the best sources of DNA. She said in the case of Sweeney's fingernails, that 73 nanograms of DNA were detected. 

Parsons asked her if she would consider that to be a large quantity of DNA. 

"I would consider it to be a large amount of DNA," she said. "The majority of the population does not have foreign DNA under their fingernails, just walking around."

She told the Crown, "I've only seen this amount of DNA in under five cases."

In his cross-examination, defence lawyer Michael Lacy disputed Dziak's earlier statement; that she had been tasked to give her scientific opinion about the male DNA found under Renée Sweeney's fingernails. He pointed out that she was rather told to look at the DNA associated with Sweeney's fingernails, which included debris that was collected at the video store and transferred into a jar with the fingernails.

'All you can say is that it came from the container'

"What we haven't heard you explain, is the major DNA donor was in relation to the debris sample," Lacy said. 

Lacy also had Dziak confirm the 73 nanograms of DNA detected, was an estimate.

Lacy also pointed to the vague nature of the phrasing, "some degree of force." He offered an example of a squirming toddler in the arms of a parent and how that could also be considered as a "degree of force."

Lacy then questioned Dziak on what she knew about the items of evidence, before they arrived to the CFS laboratory. Dziak confirmed she didn't know how they were collected or if they had been contaminated before being received by the lab. 

'An overstatement'

"You would agree ... that you cannot say that the debris came from under the fingernails of Ms. Sweeney?" Lacy asked Dziak.

"Yes I do agree with that," she said. 

"All you can say is that it came from the container," Lacy said. 

"That's correct," Dziak said.

Much of the defence's cross-examination so far in the trial, has taken aim at the mistakes made by Sudbury police during the early days of the investigation back in 1998.

Lacy moved on to ask, "You agree with me that 'it would be an absolute overstatement to suggest that the quantity of foreign male DNA associated with the fingernails is from the perpetrator of the crime."

Dziak told the court it's not more likely than any other scenario. 

Lacy said, "I'm actually reading from your evidence," referring to Dziak's letter of opinion.

"Do you agree or disagree with that statement?" he said. 

"I do agree with that," Dziak said.