Kristopher Guenther tells judge he killed Lacey Jones McKnight

Kristopher Guenther has admitted to killing his former fianc, choking her in a fight until she stopped struggling.

On trial forfirst-degree murder of Lacey Jones McKnight, the 32-year-old man testified in his own defence Wednesday in a Calgary courtroom.

• Kristopher Guenther confessed to murder, victim's mother testifies

Guenther described his relationship with Jones McKnight, which began in late 2011. The pair had an on-again off-again relationship that became rocky when she found out he was cheating on her with his ex-fiance Megan Thibault, he said.

He told the judge that on the day Jones McKnight died, she came over to his home. The pair had sex and Guenther says they participated in bondage and erotic asphyxiation. He testified that he tied her hands and ankles together using tape and rope that was later discovered in his car.

Afterwards Guenther says they fought when Jones McKnight, once again, discovered text messages on his phone to and from Thibault. Guenther said things got physical, that he put her in a choke hold and at one point realized she stopped struggling.

Showing no emotion, Guenther told the judge he then put her body in his car, wrote a suicide note on Facebook and drove to Thibault's workplace, a night club, showing her what he'd done.

After leaving the nightclub, he says he drove to an overpass in the northeast where he tried to hang himself before a passerby and a police officer saved him.

Defence lawyerKim Ross is trying to make the point that Jones McKnight consented to being restrained before she died, which could knock his first-degree murder charge downto second-degree murder or manslaughter if his testimony is believed by the judge.

Shelly Jones, Jones McKnight's mother,is in the courtroom. She told CBC News she is confidentGuentherwill be found guilty of first-degree murder.