A teenage girl was stabbed to death by her friend after the accused allegedly turned violent after smoking synthetic marijuana.

Jasmyn Tully (17) was discovered unconscious at an apartment in Tukwila, Washington, early Saturday morning. She died a short time later in hospital.

A 17-year-old male was arrested and later confessed to the crime. He now faces second-degree murder charges. The young man told officers he “felt an urge to hurt someone”.

"It appears the two individuals knew each other, were acquainted and attended school together. But right now the motive is unclear," Ian Goodhew, spokesman for the King County Prosecuting Attorney told the Daily News.

The boy's uncle told the media he had smoked synthetic marijuana, known as Spice.

"He woke up and went to the bathroom, and when he left the bathroom he said he was a changed person, and he doesn't understand what happened mentally in his mind," John Siebenbaum told KDAF-TV after visiting his nephew in custody.

Police found the suspect wandering the streets nearby with a gash in his arm. He claimed he had been the victim of a stabbing but had chased his attacker away.

The teenager appeared in court on Monday afternoon, where both the families were present.

King 5 News reports that the victim was a good student who considered the boy who was accused of her murder a friend.

Her father, Stephen Tully, said his teenage daughter was enrolled in a high school alternative program at South Seattle Community College,

“I was actually texting her when I got the call from the coroner,” he said.

“I won't ever have a moment where I won't be thinking about her. And I'm gonna miss her. I hope she didn't suffer and she's OK where she is now,” he told King 5.

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