MUNCIE, Ind. -- An eighth-grader at Wilson Middle School in Muncie, Ind., faces expulsion after admitting that he spiked a teacher's coffee with urine last Friday, according to Indianapolis TV station WRTV.

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Investigators said the student thought the incident was a prank, but school officials and police are taking it very seriously.

The boy was suspended and arrested following the incident. The school's principal said the teacher detected a foul smell and did not drink the coffee.

"Obviously, this was a very dumb thing. It also was very cruel," said Stephen Edwards, assistant superintendent of Muncie schools. "The act itself was a very cruel act."

Police and school officials were able to find out who contaminated the coffee because of help from other students. At least one student overheard other students talking about the incident and reported it.

Investigators said a vial of urine was found in the student's locker and that he eventually confessed in the case.

Only one teacher's personal coffeepot was targeted, but officials felt the matter was serious enough that they mailed a letter to parents Tuesday explaining what took place and explaining that similar incidents won't be tolerated.

"I think it's nasty and ridiculous," said parent Juanita Thomas Wilson. "Whomever the student is should be expelled from school, I believe."

The student is being held in juvenile detention and is expected to go into a diversion program.