CHICAGO - Chicago police are investigating after a baseball player at a Catholic high school in the city was allegedly sexually assaulted by several teammates last month, and 12 students have been suspended in connection with the incident, reports CBS Chicago.

A source said the alleged sex assault occurred in the locker room at St. Francis de Sales High School, according to the station.

A dozen varsity baseball players at the school were suspended Tuesday -- five of whom are accused of participating in the assault and are suspended for five days and seven others who are accused of being witnesses to the incident and not reporting it. Those students are suspended for two days.

A letter to parents said the players were accused of bullying, or failing to report bullying, but Chicago police said they were investigating the matter as an alleged sex assault, reports the Chicago Tribune.

Chicago police said an 18-year-old was allegedly attacked by five other males on March 23, at approximately 3 p.m., but the parents of the victim and the school did not report the attack to police until Tuesday, April 28. Authorities were investigating, but no one was in custody as of Thursday morning, according to the paper.

Several students who were suspended were told that although they were not directly involved in the incident, they were bystanders who failed to notify an adult or school staff member of what happened, reports CBS Chicago.

A letter sent to the parents of at least one suspended student said the individual was suspended for two days for: "Knowledge of and presence at an event in the locker room after baseball where a student was bullied; Being a bystander; Failure to report incident to an adult or staff member. This is a part of our 'Zero-tolerance' policy on bullying."

The principal of the school would only say he planned to meet with each student's parents, reports the station.

One student, a junior who was suspended two days for not reporting the incident, said what happened was typical horseplay among teammates.

"It was just a joke. It was simply a joke. We're teammates. Why would we really hurt each other?," he told the station. "We make sure that we honestly don't hurt people. We're not bullies. We don't intend to, because we're teammates. Why would we hurt our own teammates?"

"It's what we normally do in the locker room, just messing around, getting ready for the next game, tell ourselves to get ready for the next practice and all that stuff. So, I'm angry because they suspended me for two days simply for being in the locker room, at the wrong place, the wrong time, when I was grabbing my things, getting ready to get out," he added.

When asked about the alleged victim, the student said, "We don't really talk to him. We wouldn't want to get the situation any worse than it already is."

The father of another junior who was suspended five days said the kids were railroaded by school officials.

"It's wrong. The process was totally wrong. There's no investigation done to make this determination. You have one student that made a claim, and then now you have all these students suspended," he told CBS Chicago. "Basically what they are doing, is they are taking a definition of bullying, and using bullying and zero tolerance, and putting it on a group of kids for something that never happened."

The father said he does not believe an assault took place.

"I was told by a reliable source that that did not happen," he said.

Some of the suspended students showed up to school on Wednesday and were not turned away, according to CBS Chicago.

"I told them my son is going to stay in class all day, and he's going to be in this school, and he's not going to be suspended," said another father, whose son was suspended for not reporting the incident.

According to the Chicago Tribune, that father said he was told by his son that the alleged victim, age 18, was held down in the locker room while other baseball players touched him inappropriately with a baseball bat.

The Archdiocese of Chicago released a statement Wednesday afternoon saying, "The safety and well-being of students at St. Francis De Sales High School in Chicago is a top priority. Yesterday, April 28, after school administrators completed an investigation of a reported bullying incident, consequences were imposed on all students involved."