WINNIPEG -- Guilty or not guilty of second-degree murder are the two options a jury has been given in the trial of a man accused of killing a teenager and dumping her body in a river.

Raymond Cormier, 56, has pleaded not guilty to second-degree murder in the August 2014 slaying of 15-year-old Tina Fontaine in Winnipeg.

Chief Justice Glenn Joyal gave his final instructions Wednesday to the seven women and four men who will decide Cormier's fate.

"There are two distinct questions," Joyal said. "Was Tina Fontaine's death caused by an unlawful act? Did Raymond Cormier commit the unlawful act? The defence is saying you should say no to both."

Joyal told jurors that if they aren't satisfied that Tina's death was caused by an unlawful act, such as being smothered or dumped in the water while unconscious, then they must find Cormier not guilty.

Only if they are satisfied her death was unlawful will jurors have to determine if Cormier was responsible.

Joyal said just because the cause of Tina's death could not be determined, that doesn't mean her death lawful. He said evidence indicates that it is unlikely that she died of an overdose or committed suicide, since her body was wrapped in a duvet cover and weighed down by rocks.

The jury has already heard that Tina was raised by her great-aunt on the Sagkeeng First Nation, 120 kilometres north of Winnipeg, but went to the city to visit her mother. Once there, her life spiralled out of control and she became an exploited youth.

Court was told there were no witnesses to Tina's death and no DNA linking her to the accused. Experts testified they don't know how she died.

Crown prosecutors said the teen was killed and dumped in the river by Cormier, because he had found out she was only 15 after having sex with her.

During closing arguments, the prosecution pointed to audio recordings from a six-month undercover police investigation. Cormier was recorded telling multiple people he was attracted to Tina and had sex with her. Cormier also said he would bet that Tina was killed because "I found out she was 15 years old."

Cormier's lawyer argued the jury must acquit his client because there was no cause of death.

"For there to be a verdict in this case, it will be required for all 11 jurors to come to the same decision," Joyal said before he sent them off to deliberate.

"Jurors are judges of the facts. If you approach your deliberations calmly ... you will be able to reach a just and proper verdict."