BENTON CITY, Wash. — Authorities say they're investigating an attempted murder plot involving several students at a southern Washington high school.

The Tri-City Herald reports that three 16-year-old students — two boys and a girl — had plotted to kill an 18-year-old classmate on Nov. 15.

The classmate, who was not hurt, was lured to the back of a market, where they had planned to kill him with a knife.

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The Kiona-Benton City School District emergency expelled one boy and the girl the next day. The second boy's involvement was discovered this week.

Benton County Sheriff's Sgt. Bob Brockman said the older classmate was new to Kiona-Benton City High School and had "disrupted the flow" of the social order.

The boy who masterminded the plot has been held at Benton-Franklin juvenile detention center.