A mentally handicapped girl with the 'vocabulary of a toddler' was gang raped in a janitor's closet by four Florida students at North Miami Senior High School back in January, according to prosecutors.

Derek Bynum, 18, Kenoldo Alexis, 17, David Lombard, 17, and Steven Joseph, 15, are all facing a felony charge of sexual battery on a mentally disabled person.

After the alleged assault occurred near the end of the day, the girl told a security guard who saw the students leaving the closet what had happened even though she had been instructed not to.

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Derek Bynum, 18 (left), and David Lombard, 17, (right), are accused of raping a mentally handicapped girl

Kenoldo Alexis, 17 (left), and Steven Joseph, 15 (right), are also accused of taking part in the gang rape

Authorities say they raped the girl in a janitor's closet at North Miami Senior High School (above) in Florida

The teens are accused of forcing the girl, who was described by police as having the vocabulary of a toddler and was in a job-training program, to perform oral, anal and vaginal sex acts, according to the Miami Herald.

Bynum and Lombard have pleaded not guilty and the other two defendants have not entered pleas.

North Miami, which has nearly 2,400 students, expelled Bynum for 'sexual harassment' and the other boys were assigned to different schools.

'While we struggle to understand the senseless depravity of this isolated but disturbing student incident - we commend the deliberate and swift actions of Miami-Dade Schools Police in apprehending the alleged perpetrators,' Miami-Dade County School District said in a statement to NBC 6 South Florida.

Courtesy: Local 10

North Miami expelled Bynum for 'sexual harassment' and the other boys were assigned to different schools

After his arrest, Bynum wrote a note to the judge in the case.

He told the judge that he was 'really a good kid' and 'all I want to do is graduate from high school, make my family proud and be somebody'.

Prosecutors are still examining surveillance video to determine how long the teens were in the closet.

A fifth student who was initially arrested had the charges against him dropped.

An attorney for Lombard, Matthew Ladd, said: 'The discovery process is ongoing.

'We're trying to get to the bottom of what, if anything, happened - and all the clients remain and are presumed innocent.'