The Halifax jury in the William Sandeson murder trial has begun its deliberations after the judge in the case spent 3½ hours Thursday reviewing evidence from the two-month-long trial and instructing members on the law.

Nova Scotia Supreme Court Justice Josh Arnold told jurors they should come to a verdict "without sympathy, prejudice or fear." Their decision must be unanimous.

"Keep an open mind but not an empty head," Arnold said.

Sandeson has pleaded not guilty to first-degree murder in the August 2015 death of fellow Dalhousie University student Taylor Samson.

Deliberations

Arnold noted Sandeson is presumed innocent and the jury must decide whether the prosecution has proved its case beyond reasonable doubt. But he said reasonable doubt does not mean there is no doubt at all.

Jurors can find Sandeson guilty of first-degree murder, second-degree murder or manslaughter. They can also find him not guilty.

Details of deliberations are secret, and jurors are cut off from the outside world and have no access to cellphones or social media.

If members cannot reach a verdict by the end of the day, they will be sequestered in a hotel overnight and return to court Friday to continue deliberations.

William Sandeson marijuana

This marijuana was turned over to police and entered into evidence at Sandeson's trial. (Blair Rhodes/CBC)

The prosecution has alleged Sandeson was in money trouble and set up a drug deal with Samson. When Samson arrived at Sandeson's Halifax apartment, the Crown says Sandeson shot him to death and took his nine kilograms of marijuana. Samson's body has never been found.

The defence argued during its closing arguments this week that Sandeson is not a criminal mastermind and urged the jury to find him not guilty.

In the days after Samson disappeared, Sandeson told a number of different stories about what happened that night. 

William Sandeson

Sandeson is seen on a video during his interrogation by police. (CBC)

The last story he told to police during his interrogation is that two masked men came into his apartment through a window and killed Samson, taking the body and drugs away.

The judge said Thursday that if the jury believes that story, they must find Sandeson not guilty. They must also acquit him if they cannot decide whether to believe Sandeson or the prosecution.

Only if they believe the Crown's evidence can they find him guilty.

In his remarks, Arnold told jurors they shouldn't be afraid to change their minds during deliberations, but should also remain firm if they honestly believe something.

4 elements of 1st-degree murder

The judge read from transcripts of evidence heard at the trial, including the various explanations Sandeson gave about what happened that night.

The judge also reviewed evidence of possible motive, including that Sandeson's parents were upset he'd run up $72,000 on a line of credit meant for medical school, which he was to begin that fall.

He also noted evidence that Sandeson cleaned up his apartment, moved Samson's body and hid the marijuana at his brother's house.

The judge also outlined the four elements that must be proved to find him guilty of first-degree murder: that Sandeson caused Samson's death, that he did so unlawfully, that he meant to, and that the killing was planned and deliberate.

The CBC's Blair Rhodes live blogged from court.