HALIFAX -- The fate of Halifax medical student William Sandeson, accused of killing a physics student during a drug deal as part of a plan to alleviate his debt, is now in the hands of the jury.

Nova Scotia Supreme Court Justice Josh Arnold gave jurors his final instructions before deliberations began around 3:30 p.m. Thursday. They wrapped up less than three hours later, and were to continue Friday morning.

Sandeson is charged with the first-degree murder of Taylor Samson, a 22-year-old Dalhousie University student whose body has never been found.

The trial has heard Samson went to Sandeson's apartment on Aug. 15, 2015, to sell him nine kilograms of marijuana for $40,000.

In her closing arguments Tuesday, Crown lawyer Kim McOnie suggested Sandeson lured Samson to his apartment and shot him in the back of the head at his kitchen table during the deal as part of a scheme to alleviate roughly $70,000 in debt.

Defence lawyer Eugene Tan said in his closing arguments Monday that Sandeson is not a "criminal mastermind" and that the Crown twisted evidence in the case to fit its theory.

Arnold told the jury there are four possible verdicts in the case: Sandeson could be found guilty of manslaughter, second-degree murder or first-degree murder, or he could be found not guilty.

He instructed the jury on what he called a "decision tree," in which the jurors need to answer a series of questions to reach their verdict.

Those questions -- the essential elements of the first-degree murder charge -- include whether Sandeson caused the death of Samson, whether he caused it unlawfully, whether Sandeson intended to kill Samson and whether Samson's death was planned and deliberate, explained Arnold.

For example, if the jury was satisfied that Sandeson caused Samson's death, caused it unlawfully and intended to kill Samson, but were not satisfied his death was planned and deliberate, he would be guilty of second-degree murder.

If the jury answers all four questions with "yes," Sandeson would be found guilty of first-degree murder, the judge said.

Arnold told jury members their verdict must be unanimous, although they do not have to arrive at a conclusion in the same way.

"William Sandeson is presumed to be innocent until Crown counsel proves his guilt beyond a reasonable doubt," Arnold said, as Sandeson sat quietly at his lawyers bench, listening intently.

"It is not enough for you to believe that Sandeson is probably or likely guilty. In those circumstances, you must find him not guilty."

Arnold cautioned the jury not to use the fact that Sandeson may have been involved in the drug trade as evidence on the murder charge.

"It's very important that you understand that you must not use the fact that William Sandeson may have been involved in drug transactions to decide ... that William Sandeson is the sort of person who would commit the offence charged or is a person of bad character and therefore likely to have committed the offence charged," he said.

Tan has conceded there was a "violent incident" at the apartment that night, but said Sandeson maintains there was a third party at the apartment.

The trial has heard Samson was last seen alive on video walking into Sandeson's apartment shortly before 10:30 p.m. on Aug. 15, 2015.

DNA matching Samson's was recovered from a bullet, gun, duffel bag and other items seized from Sandeson's Henry Street apartment in Halifax and his family's farm in Truro, the jury had heard.

McOnie has argued Sandeson -- who was slated to start medical school at Dalhousie within a week of his arrest -- was motivated by money, noting he was in debt and that police only recovered roughly $7,200 cash.

The trial has heard Sandeson was under pressure from his parents about his spending in the weeks before he allegedly murdered Samson. Sandeson owed more than $70,000 on a $200,000 line of credit.

McOnie suggested Sandeson never intended to buy the drugs that night -- he planned to steal them.

"Taylor Samson had no clue what he was walking into," said McOnie, asking the jury to find Sandeson guilty of first-degree murder.

Tan has asked the jury to acquit Sandeson.