A Dalhousie University student on trial for murder negotiated a marijuana deal worth tens of thousands of dollars with the fellow student he is accused of killing, a prosecutor told a Halifax jury Thursday.

In her opening remarks in the case, Crown attorney Susan MacKay said police later found Taylor Samson's blood on a bullet lodged in the window frame of William Sandeson's apartment.

Sandeson is on trial in Nova Scotia Supreme Court for first-degree murder in the 2015 death of Samson. The 22-year-old's body has never been found.

MacKay said the Crown intends to introduce evidence over the coming weeks that shows the two were negotiating a drug deal leading up the death.

Samson was last seen alive on the evening of Aug. 15, 2015, MacKay said. She said he was caught on security video walking up the hallway outside Sandeson's south-end Halifax apartment.

Security video

She said Sandeson and Samson are together in the video, which is part of a security system Sandeson had hooked up to a DVR in his bedroom.

MacKay said Samson is seen in the video carrying a large black duffel bag. She said text messages between the two men will reveal they negotiated a drug deal: 20 pounds of marijuana for $40,000 in cash. MacKay told the jury the marijuana was actually worth $90,000.

Court also heard that when Samson failed to return quickly to his girlfriend as he promised, she reported him missing to police.

Samson's blood found

MacKay said when police learned of the drug deal, the case was handed to the major crime unit. She said when police searched Sandeson's apartment, they found traces of what proved to be Samson's blood, including on a bullet they found lodged in a window frame in the kitchen.

MacKay said police were contacted by a lawyer on behalf of two men, one of whom was Sandeson's younger brother. Police recovered 20 pounds of marijuana from the men and there were traces of blood on the drugs, MacKay said.

Samson's mother, Linda Boutilier, was the first witness to testify. She told court she became concerned when Samson failed to show up for Sunday dinner. She said she travelled to Halifax from her home in Amherst to join in the search for Samson. She and his friends wandered the streets of south-end Halifax, looking in hedges and dumpsters.

Worried about son's medication

Boutilier said she was aware her son sold drugs but she wasn't happy about it. She also said he had an autoimmune liver disease that required daily medication. She said she told police she was worried Samson could die if he went too long without treatment.

The rest of the first day of witnesses was taken up by police officers describing the early hours of their search for Samson. They told court how they couldn't find his phone, but were able to get the number of the last call he was on. The trail led them to a group home in Lower Sackville, N.S.

The trial in Nova Scotia Supreme Court is expected to last 32 court days.

The CBC's Blair Rhodes live blogged from court.