The room was locked from the outside with a rope tied to another door, and the boy would be kept confined inside from 6 or 7pm until 6am the following day.
The five-year-old described how he would go to the bathroom while in the room and hide the bodily waste in a hole in a wall so he would not get in trouble with his parents, according to officials.
Investigators also learned that the boy 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," the statement from the sheriff's office read.
On one occasion, the Tobiassons allegedly punished their son for eating samples at a local store when he knew he was supposed to eat carrots before eating anything else.
On August 9, the husband and wife were formally charged with one count each of second-degree child abuse.
A newly unsealed search warrant filed in the case offers additional details on the victim's carrot-based diet.
"The child was required to eat a bowl or baggy of carrots and would not be given anything else to eat or drink until the carrots were gone," the document read. "If the carrots were not eaten they would be saved for the next meal and then the next meal and sometimes the next day."
The warrant goes on to recount how one night, the family ordered pizza but the five-year-old was only allowed to eat carrots. He was given a short time to finish the carrots, with the promise that he would get pizza afterwards, but because he took too long, he was denied the takeout treat.
According to the warrant, first cited by KSL.com, Brett Tobiasson then promised his son he would give him pizza the next day, but because the child soiled his pants, he was told he could not have the pizza.
Following the parents' arrests, their adopted son was taken to a doctor's office, where a nurse who examined him noted that he had an 'orangey' tint to his skin, apparently caused by an excessive consumption of carrots.
The Daily Herald reported that Clarissa Tobiasson told a friend last year that she forced the boy to eat carrots because she knew he did not like them.
The court documents also revealed that the boy would bump into walls in the dark basement, and that he told officials he was scared to be there because there was a mouse and spiders in there, and the floor of the subterranean room was littered with mouse feces.
When interviewed by police, Mrs Tobiasson reportedly told detectives she did not know she could not lock her children in their rooms.
The child, who is now six years old, was adopted by the Tobiassons along with his biological two-year-old brother. The couple also have their own biological two-month-old baby daughter.
The six-year-old boy is currently being cared for by a grandmother. His younger brother and the Tobiassons' infant daughter are in the custody of the Division of Child and Family Services.
The Tobiassons are currently out on $10,000 bond each and are due back in court on September 14.
