SEATTLE -- Documents and interviews with neighbors are offering clues about the possible motive for a 17-year-old's alleged slaying of a Bellevue high school tennis coach, KIRO 7 Eyewitness News reported.

Slideshow: Images From Seattle Shooting Case

Samson Y. Berhe, who turns 18 on Thursday, was ordered detained at a hearing Tuesday in juvenile court. He was arrested Monday after he was found on a barge across the Duwamish River from the shooting scene.

HOW TO HELP A scholarship fund has been set up for 14-month-old Louisa Robb. Contribute at any Washington Mutual Bank branch.

Michael Robb, a tennis coach at Newport High School, was shot in the face Sunday night as he sat in his car on West Marginal Way in Seattle. Witnesses said a male approached the car and fired a shotgun through the open driver's side window, then ran toward the river

Neighbors told KIRO 7 Eyewitness News the teen said he had a grudge against white people.

"He always say that he (was) gonna kill all the white people in the world," said Anna Bell Perkins. "Samson had, like, some sort of complex against Caucasian people. And he said he wanted to kill them all and told me I could watch," said another neighbor.

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Video: Newport High Grieves For Popular Coach

According to court documents, Behre owned a shotgun. Police cut down a tree from his yard and recovered a bullet of the same caliber used to kill Robb.

An hour before Robb was shot, Berhe was investigated and released for a burglary near the shooting scene, police wrote in court papers.

The King County prosecutor's office said it planned to file charges by Thursday.