A 29-year-old B.C. man has confessed to slashing his five-year-old stepdaughter to death at a vacation home in Washington State.

According to papers filed in a Washington court Monday, Peter James Wilson admitted to police he cut the throat of Clare Shelswell Sunday night after an argument with the girl's mother, Sarah Wilson, near Lake Cushman, west of Seattle.

In Pictures: Washington State Murder

Officers responded to a frantic 911 call from the home around 6 p.m. and found the little girl inside with her neck slashed with a kitchen knife.

Sarah Wilson told police the couple was arguing about disciplining the child and Wilson told her "not to worry" and "he would take care of it."

The girl's mother said she rushed to the kitchen after hearing a scream and found her young daughter and her husband both covered in blood. The little girl was lying on her back clutching at her neck.

Deputies found Wilson on a swing in a gazebo outside the home. He was arrested is now being held for first-degree murder. The girl died at the scene.

Officers were told by the family Wilson is taking medication for bi-polar disorder.

"I've been doing this for 37 years and this is absolutely the most horrific event that I can think of happening," said Chief Deputy Dean Byrd of the Mason County Sheriff's Dept.

In a statement sent to media Monday afternoon, Sarah Wilson said her husband was responsible for her daughter's "brutal" murder and thanked the medical personnel who came to her aid after the incident.

"God's richest blessings on you all for the amazing compassion and heart you have shown to me and my family during this time," she wrote. "The family gratefully accepts all offerings of prayer and love."

Wilson was held overnight in Mason County jail in Hoodsport. He appeared briefly at Mason County Superior Court in Shelton, Washington, for a bail hearing Monday. Bail has been set at $3 million US.

His next court appearance is scheduled for July 12.

Lake Cushman, a popular camping and hiking destination, is located west of Seattle in the Olympic Peninsula. Detectives say the B.C. family had only been staying in the area for a few days before the girl's death.