A Chicago police officer, Eugene Ciardullo, who also worked as a security guard at a high school has been charged with having a sexual relationship with an underage girl who attended the school.

The police officer, 51, was charged with one felony count of criminal sexual assault of an underage girl between 13 and 17 years old. The student, now 18, allegedly acknowledged that she had a sexual relationship with Ciardullo.

Ciardullo allegedly befriended the victim during the 2014-2015 school year, when the girl was a 16-year-old sophomore.

The relationship began to grow

Ciardullo and the underage girl exchanged phone numbers, they chatted on social media during the summer after her sophomore year.

In September 2015, Ciardullo allegedly told her through Snapchat that he had feelings for her. 

The relationship became physical and carried on from February through December 2016, with Ciardullo meeting her, then 17, for sex in an empty parking lot and in motel rooms.

Ciardullo, a Marine Corps veteran, began personally training the girl in preparation for a physical fitness test to enter the Marines, assistant state's attorney Ed Murillo said.

Ciardullo was cautious about the relationship

Both discussed their age difference, and Ciardullo told the girl that he "could lose his job and go to jail if they were caught," Murillo said.

Ciardullo told the underage girl to "tell people who asked about their relationship that they were just good friends."

One of the girl's relatives confronted the police officer in late November after learning of a text exchange between the girl and Ciardullo, and the police officer admitted they were having a relationship, Murillo said.

The police officer will have to face the consequences

Police arrested Ciardullo on Friday, and he allegedly admitted to having an affair with the girl.

Ciardullo's bail was set at $75,000, and a judge has barred the police officer from having contact with the victim or anyone who is underage.

The Chicago Police Department is investigating the case administratively and internally.