A man named Derek Jensen was the shooter in a murder-suicide that left four people dead on an Alberta highway, CBC News has confirmed.

Jensen was an ex-boyfriend of one of the female victims, Tabitha Stepple, according to media reports.

Among the dead were Tanner Craswell, 22, and Mitch MacLean, 20, baseball teammates and best friends originally from P.E.I. and known as promising athletes. Stepple, one of two women travelling with the ballplayers, was also killed in the attack.

"This one was particularly horrific. We had so many people shot, so much tragedy there," said RCMP Sgt. Patrick Webb.

Jensen was found dead at the scene on Highway 2 after turning the gun on himself.

Alberta RCMP have been piecing together the murder-suicide, which unfolded near Claresholm early Thursday morning. They suspect the killings were targeted and related to a domestic dispute.

"This is not a random. This is not a stranger shooting," Webb said Friday morning.

RCMP provide member support RCMP spokesman Sgt. Patrick Webb said the force is offering support to its members who may have been affected by the traumatic nature of the multiple fatal shooting that happened on an Alberta highway early Thursday morning. Webb said roughly 15 members were at the scene, including detachment members, major crimes unit, identification section and traffic control. Webb said there will be a critical incident debriefing on Monday to aid any of the officers with their emotional and mental health. Webb said it was a particularly horrific crime, due to the age of the victims, number of deaths and the nature of the apparent murder-suicide. Members will be given an opportunity to speak with psychologists about what they saw and what they did to help cope with what happened, he said.

The only survivor in the attack was Shayna Conway, formerly of P.E.I., who is recovering in hospital.

Webb said investigators are hoping to speak with Conway as she recuperates from the ordeal.

"We actually have an eyewitness, someone who was on scene and knows exactly who was there and exactly what happened," he said. "We're working with her so that she's in a state she can help us."

Police, following up on reports of gunfire, came across a car and an SUV in a ditch and discovered three bodies and two injured people. One man died later in hospital.

Probing 'every possible detail'

RCMP released few details about their investigation, but said officers had recovered a gun and expected to release more information in coming days.

"Our investigators on scene, what they're doing is looking back at every possible detail. Literally in the seconds, hours, minutes, days before this happened on that highway," Webb said Friday.

He confirmed that among the details being probed is how an earlier encounter at a 7-Eleven store may have played into the deadly incident.

Police have seized surveillance footage from the shop and are reviewing it for clues.

Shayna Conway, formerly from Charlottetown, is expected to survive her injuries. (CBC)

"Yes, there was something that happened at the convenience store, but we want to get the story from our lone survivor," Webb said.

Craswell and MacLean, along with the two women, had been en route to the Calgary airport before the shootings.

Friends mourn deaths

Kevin Kvame, the manager of the Lethbridge Bulls baseball team on which the two young men played, said the pair had set out for a two-hour road trip to the airport so they could fly home to P.E.I. for Christmas. A girlfriend had agreed to drive them, and was accompanied by a female friend, Kvame said.

In an interview Friday with CBC Radio's Calgary Eyeopener, Kvame said Tanner had just celebrated his 22nd birthday on Wednesday night.

"That was one of the reasons he ended up lining up transportation to go to Calgary that time of the day," he said. "Because he was out celebrating his 22nd birthday and wanted to go up with his girlfriend and her friend. I'd offered to take them up earlier if they wanted to go, but they wanted to be with their friends that last night in the city before they went home."

People in Charlottetown and Lethbridge are mourning the deaths of the two ballplayers. Friends in Alberta told CBC News they'll remember two kind guys who loved baseball.

Tanner Craswell, 22, and Mitch MacLean, 20, were both originally from the Charlottetown area. (College of Southern Idaho Athletics/Pointstreak)

In Charlottetown, Matt Hood, who grew up with Craswell and MacLean, said they shared a love of baseball. Hood said even the snow didn't stop the two ballplayers from giving Hood's younger brothers a practice session.

"Tanner and Mitch would have a catch with them in the dead of winter with snow up to their shins … just to help them out," he said. "That's the kind of people they were."

Allison MacDonald, who coached MacLean on the Islanders baseball team in the summer of 2010, said MacLean was preparing to head to the U.S. to play college ball this winter.