FRANKLIN PARK, Ill. (CBS) — A student stood charged with attempted murder Thursday after police said he stabbed a classmate at East Leyden High School in Franklin Park.

Leyden High School District 212 Supt. Dr. Nick Polyak and Franklin Park police Director Mike Witz issued a joint letter Thursday that was posted on the school district website.

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The letter said, as police reported previously, that one student was stabbed by another during a passing period in a hallway at the school at 9:30 a.m. Tuesday. The stabbing followed a quarrel that had erupted in class days earlier that culminated in the violent confrontation, the letter said.

The victim’s brother previously told CBS 2 the attacker might have threatened the stabbing in a social media post.

The entire confrontation lasted about 10 seconds, the letter said. Within five seconds afterward, the student who was injured received medical care from the school’s resource officer, dean, and security staff, and was rushed to the school nurse’s office and then to the hospital, the letter said.

“Those staff members and first responders should be credited with saving that student’s life through their quick actions,” the letter said.

The building was placed on lockdown, and the student suspected in the attack was arrested by Franklin Park police and was charged with attempted murder, police said. Cook County prosecutors said a Juvenile Court judge ordered him held in custody. He was due back in court on Oct. 23.

Franklin Park police have concluded that the attack was not gang-related. Students were sent home for the day following the Tuesday stabbing, and the school reopened as usual Wednesday.

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But that day, police and school officials became aware of several social media threats that contained gang references. Some were posted by former Leyden students, some by current students, and some were anonymous, the letter said.

The school received more than 100 tips from students on an anonymous tip line, the letter said.

School administrators and local police worked through the night Wednesday into Thursday to investigate. The administrators decided to close the school for the day and have an e-learning day on Thursday, while the officials held a meeting at the school about the investigation of the social media posts.

The meeting included representatives from the Cook County Sheriff’s police and the police departments in Franklin Park, Melrose Park, Northlake, River Grove, Rosemont, and Schiller Par, as well as representatives from Leyden Township and suburban village government, the letter said.

The school and police have identified more than 40 students and families responsible for the social media posts over the past 24 hours, and local police and school officials are addressing them, the letter said.

“Again, I cannot comment on the specific outcomes, but I can say that those issues have been addressed,” Polyak wrote. “Those processes have yielded the conclusions that there is no credible threat from those posts.”

Police and school officials also determined that some students knew ahead of time that the fight in which the student was stabbed on Tuesday was going to happen, but did not report it, the letter said.

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On Friday, East Leyden will reopen for classes. Counselors and social workers are available as usual in Room 217, and there will be an increased police presence both inside and outside East and West Leyden high schools, the letter said.