An inmate used a razor blade to cut another prisoner at Rockview state prison last week, state police at Rockview said.
Police said the razor blade was melted into the end of a toothbrush, and the inmate brought it into the dining hall, slicing the other inmate.
The inmate who was cut suffered an injury that required stitches, police said.
The incident occurred at about noon Dec. 22.
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Police said the investigation is ongoing.