Police and school officials were on high alert Wednesday looking out for possible retaliation after a student was slashed at Spring Valley High School Tuesday.

Christopher Bermeo, 16, was charged as an adult with attempted murder after police say he attacked a 17-year-old student in a hallway at around 9 a.m. Bermeo stabbed the victim four times with a knife that looks like a pen, according to police. The victim is expected to be OK.

In court, Bermeo pleaded not guilty. He claims he was being bullied and says he was defending himself at the time of the stabbing.

School officials say extra police will patrol the campus until further notice.