TORONTO -- A man accused in the death of a York University student from China sexually assaulted the young woman in a "disturbing" attack, his lawyer acknowledges, but he did not mean to kill her.

Brian Dickson, 32, has pleaded not guilty to first-degree murder in the death of Qian Liu, but his lawyer urged the jury in closing arguments Friday to find Dickson guilty of manslaughter.

"His actions are despicable," Robert Nuttall told the jury. "I'm not trying to excuse them. He's not walking away."

But for the jury to find Dickson guilty of first-degree murder they must be satisfied he either meant to kill the 23-year-old student or cause her bodily harm that he knew was likely to cause death.

Nuttall suggested Liu's death was an accident amid a bizarre sexual assault -- partly witnessed by her ex-boyfriend via webcam.

The pathological and DNA evidence fits with a scenario of Dickson sitting on her chest while he was "sexually excited" with her neck cricked, Nuttall said.

"How could you infer from that that he knew sitting on her chest and perhaps with her neck and her head at an awkward angle would cause somebody to die?" Nuttal asked the jury. "Would any of you know that?"

One forensic pathologist concluded Liu's cause of death was unascertained, though mechanical asphyxiation -- which could include neck compression -- was the best overall explanation. A second forensic pathologist definitively concluded it was mechanical asphyxiation.

Liu had been chatting via webcam with her ex-boyfriend in China in the early morning hours of April 15, 2011, when she answered a knock at the door of her room in the basement of an off-campus building. Dickson, who was not a student, was one of several other tenants in the house.

The ex-boyfriend, Xian Meng, testified that the man at the door appeared to ask Liu for her cellphone, which she retrieved for him. He pushed some buttons and they were speaking in a friendly way, then the man tried to embrace her and Liu tried to push him away, Meng testified.

But he forced his way inside while Liu was pushing at his chest and saying "no," Meng testified. The man pushed Liu down off camera and after the sound of two muffled bangs Meng said he heard no more sounds from Liu.

After a period of silence he heard the man breathing heavily and moments later the man appeared naked in front of the webcam and turned off the computer, Meng testified.

The jury should have no difficulty finding that Dickson sexually assaulted her and it caused her death, Nuttall said in his closing arguments.

"This is despicable conduct," Nuttall said. "It's disturbing conduct. It's blameworthy conduct. But I suggest to you that it doesn't support the necessary inference beyond a reasonable doubt...that Mr. Dickson had murderous intent."

The Crown argues that Dickson forced himself on Liu, which is what Meng witnessed via webcam, then killed her to cover it up.

"Mr. Dickson forced his way into Ms. Liu's apartment to attempt to have some sort of sexual encounter with her," Crown attorney Christine Pirraglia said in her closing arguments.

"When she resisted he was caught by the potential discovery of his actions. At that point he had motive to silence her and to kill her. That's what we suggest happened in this case."

Nuttall suggested that the Crown's motive theory defies common sense.

It happened in Dickson's own building with other tenants around, including others occupying other basement apartments, Nuttall said. Would he really take that risk, Nuttall asked.

Did Dickson think, "I'm going to commit murder because I don't want anyone to know I was fooling around with her without her consent?" Nuttall said.

"There's a lot of difference between getting caught for trying to steal some sex and getting caught for murder."

Liu was found dead mostly naked and face down on the floor of her room. An earring was missing from one ear, her nightgown was rolled up to her chest and her underwear and tights were in the corner of the room. Semen was found on her thigh and groin and a bodily fluid likely either semen or saliva was on her breasts, Pirraglia said.

"Does that leave you with any doubt whatsoever that when Mr. Dickson tried to embrace Ms. Liu and pull her toward him that he was sexually assaulting her?" Pirraglia said to the jury.

The semen, which a forensic biologist testified matched Mr. Dickson's DNA to an astronomical probability, was not deposited on Liu until after she was dead, Pirraglia suggested.

In Nuttall's chest-sitting scenario, the fluid on her breasts could have been because Dickson's genitals were in that area, he said.

It's a case that turns on the pathological evidence, he said.

If Liu died of mechanical asphyxiation because Dickson choked her, "it wouldn't take a genius" to infer a murderous intent, Nuttall said.

But the two forensic pathologists who testified disagreed as to whether bleeding inside Liu's neck muscles was a result of trauma to the neck or just pooling of the blood after death.

If the bleeding happened before death, that would rule out Nuttall's chest-sitting scenario, one pathologist testified.

"In the face of two different opinions as to whether what we're seeing could be real bleeding or pooling, in all good conscience how can you say, 'I'm satisfied that the mechanism of death, pressure on the neck, is so well established in the evidence' as to be sufficient for you to draw the inference of murderous intent?" Nuttall said.

The case is expected to be in the jury's hands on Monday.