HALIFAX -- Accused murderer William Sandeson was polite and co-operative when first questioned by investigators, a Halifax officer testified Monday as the jury was shown a video of the medical student's initial police interview.

RCMP Sgt. Charla Keddy testified that Sandeson was not under suspicion when she interviewed him on Aug. 18, two days after Taylor Samson, a Dalhousie University physics student, was reported missing.

Keddy told the Nova Scotia Supreme Court jury that Samson's case had not yet been deemed a homicide, but his drug-dealing had heightened concerns about his disappearance.

She said she was assigned to follow up on a phone number that had been linked to Sandeson -- the last number retrieved from Samson's phone.

Keddy said Sandeson, 24, agreed to come to the police station, where investigators took photos of messages on his cellphone.

The jury was shown a 100-minute police video that shows Sandeson casually dressed in a T-shirt, shorts and ball cap, sitting on a black couch in an interview room at the station.

In the video, he tells Keddy the last time he saw Samson, 22, was Aug. 13 -- two days before he went missing -- and that he had been introduced to Samson about three weeks earlier for the purpose of buying marijuana from him for personal use.

Sandeson told the officer that when they met on Aug. 13, he didn't like the quality of the marijuana, but Samson later sent a text message to say he had better quality weed to sell.

The accused then told the officer he had sent text messages to Samson on Saturday, Aug. 15, but said the two never met face to face.

"He didn't respond to a text on Saturday night. I texted him Saturday night and I texted him again Sunday," Sandeson told Keddy during the interview, appearing friendly and calm.

"No response."

Sandeson told Keddy that he was looking for only a couple grams of marijuana for himself, but that he knew people who wanted to buy larger quantities.

"I know people who are looking for pounds. I was curious -- if he had a good price on something, I could put him in contact with them," said Sandeson, telling the officer that never happened.

The Crown alleges last time Samson was seen alive, he was recorded on a surveillance video walking into Sandeson's apartment to sell 20 pounds of marijuana to the accused for $40,000.

Sandeson was charged with first-degree murder on Aug. 20, 2015, four days after Samson was reported missing. His body has yet to be found.

Also Monday, Frances Mysketyn-Driscoll, who worked with Sandeson at a group home in suburban Lower Sackville, said he came in to work coughing on Aug. 16, 2015, saying he had been doing a lot of cleaning the night before, and had inhaled bleach.

Originally from Truro, N.S., Sandeson is a former varsity track athlete who was set to start his medical studies within a week of his arrest.

The trial will resume Thursday morning.

In an opening address last week, Crown lawyer Susan MacKay said evidence will show that police detected DNA matching Samson's genetic profile on a gun and a bullet found in Sandeson's apartment in Halifax.

MacKay said the gun was found after police made an emergency entrance into the apartment "because they were concerned that Mr. Samson was being held hostage there" after officers read text messages between the two Dalhousie University students.