The mother of a 7-year-old elementary school student in Flint, Michigan, is speaking out after a police officer handcuffed her son and subsequently lost the key on October 12.

Chrystal McCadden received a call from Brownell STEM Academy to pick up her son after he reportedly acted out, but when she arrived, McCadden found the child handcuffed and standing alone in a hallway, with his hands behind his back.

Her son, Cameron, was previously diagnosed with ADHD, McCadden said, and the school would sometimes call her when he became disruptive. But she was shocked to learn that Cameron was allegedly threatened by an officer who said he would handcuff the 7-year-old if he didn't sit down as the officer requested.

The officer followed through with his threat and handcuffed Cameron. When McCadden asked for the handcuffs to be removed, however, she was told that the officer didn't have the keys.

"You put my son if handcuffs and you didn't have the key," McCadden told NBC News. "He wasn't in here with a gun or knife. There was no other action you could do?"

"While police later claimed that they handcuffed the boy for his own safety, when the mother pressed for answers, she said that the school and the police said very little until she got the media involved," the New York Daily News reported.

In a statement, Flint Police Chief James Tolbert said "I have apologized to the mother for this situation and assured her that we will protect the integrity of this investigation and will be transparent in our findings."

"It is our model to engage children in a positive light that will foster trust and respect, this incident does not reflect positively on that model," he added.