A man from Airdrie, Alta., has admitted to strangling his common-law wife and burning her body in an abandoned building because he wanted to go drink beer at Boston Pizza with a friend.

Duane Redelback pleaded guilty to manslaughter on Thursday in the 2006 death of Ruth Degayo, whose burned body was found in an abandoned building in Exshaw, about 20 kilometres east of Canmore.

Nearly a decade after the homicide, Redelback told two undercover officers that he and Degayo had a fight on the night of Jan. 7, 2006, because she wanted to go to the mall and he wanted to have beers with a friend, according to an agreed statement of facts.

Degayo strangled and suffocated

Redelback said he wrestled the couple's son, who was two at the time, from Degayo and put the boy in his bedroom.

The couple continued to fight and Redelback said he strangled and smothered her until she stopped breathing.

He tied her up, placed her body in a garbage bag and stuffed her into a suitcase that he put in the trunk of his car.

He then went to Boston Pizza for drinks with a friend, leaving the child alone.

Duane Redelback admitted to strangling and smothering his common-law wife because she didn't want him to go drinking with a friend. (wayn.com)

Redelback then drove back to his house to check on his son before heading to the abandoned building in Exshaw where he doused the suitcase in gasoline and lit it on fire.

"The f**king flames were like 30-feet high," said Redelback to undercover officers.

After he returned home, Redelback covered his tracks by getting rid of his shoes and tires.

Case goes cold

Degayo's remains were found on Jan. 8, 2006, the same day her killer reported her missing to RCMP.

DNA tests determined the remains were those of 40-year-old Degayo, but the case went cold.

It wasn't until 2015 when RCMP initiated the undercover operation that involved more than 40 "scenarios" designed to build trust between the officers and Redelback that officers were able to get a confession.

Originally, Redelback was charged with second-degree murder and indignity to a human body.

Prosecutor Jim Sawa and defence lawyer Balfour Der worked out a plea to the lesser offence of manslaughter.

'If only I could exchange my life for her'

Degayo's father, who lives in the Philippines, thanked the Canadian government, the RCMP and the prosecutors "who helped find justice for our beloved daughter Ruth," in a victim impact statement read aloud in court.

Ronie Degayo is a farmer and a fisherman in the Philippines. His family did not have a lot of money but said after graduating college, Ruth set out to get a job, first in Singapore and then in Canada. She sent money home for her six siblings so they could also get a higher education.

"I miss my daughter dearly, I did not expect that her life would end this way," he wrote. "If only I could exchange my life for her."

Riza Fornier, a registered nurse in Orlando, Fla., was Degayo's only sister.

"She taught me to be brave," said Fornier. "My family will suffer this loss and pain for the rest of our lives."

"Only a heart so dark, so ruthless, so evil could do that."

'She tried her best to survive'

Degayo was in a car accident while pregnant, causing her to go into early labour. Her son Justin was born prematurely and suffers from Cerebral Palsy.

Fornier said Degayo's relationship with Redelback was tumultuous and she feared for her safety at times. She once went to a neighbour's for help and attended a local shelter with her son.

"She tried her best to survive for her beloved son."

Court of Queen's Bench Justice Karen Horner accepted a joint recommendation of a 15-year prison sentence proposed by Der and Sawa. He gets two years credit for the time he's already served.