The girlfriend of an Alberta man charged with the first-degree murder of a young mother says he believed he would be killed if he didn't "deal with" a former gang member in Saskatoon.

The prosecution contends that Lorry Santos, a 34-year-old mother of four, was shot in a targeted hit that turned out to be at the wrong address.

Randy O'Hagan of Lloydminster, Alta., is on trial in the fatal shooting, which took place in the early morning of Sept. 12, 2012.

Santos was on maternity leave at the time after having her fourth child.

Her husband was getting ready for work, and it's believed Santos was shot through her living room window as she went to answer the door.

O'Hagan's girlfriend testified Tuesday that he told her his boss in the White Boy Posse street gang ordered him to go to Saskatoon to kill a former member or be killed himself along with his family.

The woman said she started dating O'Hagan in 2011 and sold drugs in Lloydminster to feed their severe oxycodone addiction.

She said she saw a text on a drug phone about a month before Santos was killed saying there was a $40,000 hit on someone's head in Saskatoon.

She said the drug boss also threatened to cut her head off and take it to her parent's doorstep if she didn't convince Hagan to do what he wanted.

"He ruined our lives," she said, wiping away tears.

The two blew kisses to each other as O'Hagan mouthed the words "I love you" from the prisoner's box.