Clarissa Anne Tobiasson
Brett Parker Tobiasson and Clarissa Anne Tobiasson have both been arrested on child abuse chargesUtah County Sheriff's Office

A married couple from Utah have been arrested after police say they kept their five-year-old adopted son locked in a windowless basement without light, access to food or a bathroom.

Investigators say Brett Tobiasson, 31, and wife Clarissa, 27, would lock their child in the tiny, pitch-black room at their Eagle Mountain home for 12 hours at a time, with only a mattress and blanket as company.

The boy described how he would have to go to the toilet next to where he slept and put the waste in a hole in a wall so he wouldn't get into trouble.

In what Utah County Sheriff's Office said was a clear case of child abuse, investigators told of how the child was fed a diet that consisted largely of carrots.

"He would be required to eat carrots before every meal and if he did not finish them within a certain time limit he would not be allowed to eat the rest of the meal," a statement from the Sheriff's Office said.

"In another instance he was disciplined for eating samples at a local store when he knew he was supposed to eat carrots before eating anything else."

Brett and Clarissa Tobiasson were both arrested for felony child abuse on Thursday (3 August), with investigators accusing them of having "intentionally inflicted serious physical injury on their five-year-old son".

The arrests came after several months of investigation where workers with the Utah Division of Child and Family Services (DCFS) interviewed both witnesses and the alleged victim in the case.

"Investigators learned that the six-year-old boy, who was five years old when the crime occurred, would be locked into a basement room that was about 10' x 10'," the Sheriff's Office said.

"The room had no light and had a loose carpet covering the floor.

"The boy had only a mattress and a blanket to sleep with. That room was locked from the outside and the boy would be locked there around 6.00-7.00pm and would not be let out until after 6.00am in the morning. The room had no light and had a loose carpet covering the floor."

The alleged victim was adopted by the Tobiassons along with his two-year-old brother. The couple also have a two-month-old daughter.

The alleged victim in the case is in the care of a grandmother, while the other two children are in the custody of DCFS.

The Tobiassons are currently in jail with bail set at $10,000 cash or bond.