The cousin of the man charged with murder in the death of a Dartmouth cab driver testified Monday that Chaze Thompson fired a single shot in the back of the victim's head, in January of 2009.

Thompson, 22, is charged with first-degree murder in the death of taxi driver Sergei Kostin, a long-time driver who moved to Canada from Ukraine.

Testifying in a Nova Scotia Supreme Court in Halifax, Thompson's first cousin, Wayne McAvoy, said he first met Thompson the summer before Kostin disappeared. He said the pair began hanging out two or three times a week listening to music, talking about girls and smoking weed.

The court heard Thompson showed McAvoy a gun about a month and a half before Kostin was killed. McAvoy described it as black, with a sawed-off barrel and a grip wrapped in electrical tape. The next time he saw the gun, he said, is when Kostin was killed.

McAvoy recounts day Kostin was killed

The day Kostin disappeared McAvoy said he walked two kilometres with Thompson to a convenience store to call a cab. He described how a green car Chevrolet Impala from Bob's Taxi picked them up to drive to Cherry Brook.

McAvoy told the court that when Kostin told them the fare he could hear clicking from the back seat where Thompson was sitting.

Then he heard a gun shot.

McAvoy said the cab driver slumped forward, a bullet wound in the back of his head and blood pouring out of his mouth, nose and ear.

He then described how his cousin in a calm but demanding voice ordered him to drive the cab, with Kostin's body in the backseat and the driver's seat covered in blood.

McAvoy said he drove because he was afraid he'd be shot if you didn't comply.

Kostin was reported missing in January 2009, after he was last seen picking up a fare at a variety store on Gaston Road in Dartmouth (Courtesy Halifax Police)

As the cab was stopped at a stop sign, McAvoy said an RCMP car sped down Highway 7 toward Dartmouth.

Thompson told McAvoy to pull over to the side of a deserted stretch of Upper Governor Street. McAvoy said Thompson started dragging the body of the cab driver into the woods.

After dragging the body for about three metres into the woods, McAvoy said Thompson called him over to help. McAvoy said he picked up the legs and carried the body to a spot where a fallen tree was lying.

He said after dragging the body into the woods, Thompson had him drive the cab to a spot where it was later found by police, abandoned.

Thompson and McAvoy started walking until, he said, Thompson flagged down a car to get a drive back to Dartmouth.

McAvoy said he didn't recognize the two men giving them a drive back to Dartmouth, but he said during the drive, Thompson asked them if they knew how to burn a car. Kostin's cab was found gutted by fire.

This gun matches that used to kill Sergei Kostin. (Blair Rhodes/CBC)

During the drive, McAvoy said Thompson asked the other two men if they wanted to buy a gun. McAvoy said Thompson told them there were "a couple of bodies on it."

McAvoy said he noticed blood on the backs of the legs of the white sweatpants he'd been wearing, where his legs brushed against the seat of the cab.

Thompson told him to take his clothes off. McAvoy took a shower. When he came out, he said his clothes were gone.

McAvoy expected on stand all week

McAvoy is expected to be on the stand most of this week and face an especially tough cross-examination from Thompson's lawyer.

Twenty-five days have been set aside for the trial. Four have been used so far.

McAvoy went to police in April 2009 with a statement and led them to the body. He was granted immunity.

Last week a police witness testified that there was no evidence found on Kostin's body or the burned-out remains of his cab that ties Thompson to the crime.

On April 1, 2009, Kostin's body was discovered in woods off Upper Governor Street in North Preston, about a kilometre from where his cab was found. Police have not said how Kostin died.

Kostin had no family in the Halifax area — his wife and other relatives live in his native Ukraine — and he was a driver for Bob's Taxi for about 10 years.

Thompson was charged in January 2010, almost a year after Kostin was first reported missing.