02/18/2015 05:23 EST | Updated 04/20/2015 05:59 EDT

Kristopher Guenther's trial begins in death of Lacey Jones McKnight

A Calgary man accused of first-degree murder confessed several times to killing his former fiancée on the night she died, a lawyer for the prosecution told court as the trial got underway on Wednesday.

In his opening statement, Crown prosecutor Joe Mercier told Justice Alan MacLeod that Lacey Jones McKnight and Kristopher Guenther had been engaged, but their relationship had become volatile in late 2012.

On Oct. 25 that year, Jones McKnight drove to Guenther's home where they fought, Mercier said.

Guenther told an ex-girlfriend that when he and Jones McKnight began fighting, he tried to choke her several times before tying her hands and feet together and duct taping her mouth.

Guenther also put a plastic bag over Jones McKnight's head and while she was crying, choked her again until she was lifeless, court heard.

Mercier told the judge that Guenther then drove to an ex-girlfriend's workplace where he showed her Jones McKnight's body in his car.

After that, the Crown says Guenther drove to Jones McKnight's mother's home where he gave her a knife and asked her to kill him before telling her he had killed her daughter.

When she refused, Mercier says Guenther drove to a nearby bridge and tried to hang himself before passers-by called 911 and first responders pulled him to safety.

Jones McKnight's body was found in the nearby car and Guenther was arrested for murder.

He has been in custody ever since. The Crown is pursuing a first-degree murder conviction partly because the killing involved confinement.

Since her daughter's death, Shelly Jones has been vocal about her frustration with police, who she believes did not take the family's concerns about Guenther seriously.

"In the weeks leading up to her death, we called police six times asking for help," said Jones. "She paid the ultimate price for their negligence."

The prosecution expects to call about 50 witnesses during the trial, which could go as long as five weeks.