HALIFAX -- Accused killer Nicholas Butcher appeared "calm" as paramedics treated him the morning Kristin Johnston was found dead, despite having an amputated hand and 13 penetrating wounds on his neck, a Halifax jury heard Wednesday.

Paramedic Sean Collins testified at Butcher's second-degree murder trial that he rode with Butcher, 35, in the back of an ambulance en route to hospital from the Montreal-born yoga instructor's Halifax-area home on March 26, 2016.

Collins said Butcher appeared "upset, but calm," noting there were lacerations on his neck and on the wrist of his remaining hand.

"He kept asking to call his mom," said Collins.

At the hospital, Butcher was taken to an operating room, the 14-member Nova Scotia Supreme Court jury heard.

Dr. Jonathan Trites, a head and neck surgeon, said Butcher had 13 sharp wounds on his neck: Seven in the centre, and three each on the left and right sides of his upper neck. He said none were longer than three centimetres.

Trites agreed with defence lawyer Peter Planetta that if left untreated, the neck injuries would have been potentially life-threatening.

He noted an injury to Butcher's trachea went in at a steep angle, not straight in.

The jury heard earlier this week that Butcher told a 911 dispatcher he had killed his girlfriend and tried to kill himself.

Another paramedic, Sarah Grace Brown, described Butcher as appearing "relatively calm" after she arrived on the scene in Purcells Cove.

Brown said she was tasked with retrieving his hand, so she went to the house and asked police for it.

She said an officer argued it was part of the crime scene, but she reiterated she needed it, so the officer went and retrieved it for her.

Brown said she brought it to the ambulance, shielding it from members of the public who had started to gather outside the home.

She wrapped it in sterile gauze and then put it into a sterile bag.

Police officers have testified they found Johnston's body in the master bedroom of the home on a blood-soaked bed, next to a steak knife.

They testified that a mitre saw and an amputated hand were found nearby.

Butcher has pleaded not guilty.

Witnesses have testified that Butcher was living with Johnston, 32, at the time of her death, and that she had broken up with him hours earlier.

Harry Lehmann, who lived in a basement unit of Johnston's house, testified he woke up around 4:30 a.m., and heard "shoes coming off" upstairs just after 5 a.m. He made an assumption that Johnston and Butcher had just arrived home.

"And then it was quiet after that," said the 57-year-old Winnipeg man, who was staying in Halifax for a few months at the time of Johnston's death.

Lehmann says around 7 a.m. he decided to do laundry in their shared laundry and storage room.

About a half hour later, he heard someone coming down the stairwell and then rummaging in the storage room before hearing something dragging along the floor. He likened the sound to the prongs of a cord.

About five minutes later, he heard a "humming, mechanical" noise. He thought it sounded like a microwave.

Soon after that, he heard sirens, and then someone coming down the stairwell to his apartment. It was a police officer, who detained him.

He was released after being questioned by police, and said he learned of Johnston's death on the news.

The trial continues Thursday with more testimony from Crown witnesses.