The trio, whose names had not been released, had not been charged, The Kansas City Star reported, but investigators had turned their findings over to Clay County prosecutors.
A police report stated officers found the 17-year-old youth in a fetal position cuffed to a steel pole in a home's basement Feb. 4 after getting a call from a concerned neighbor.
The boy, who police described as "very thin" and wearing dirty clothes, said he had been locked in the basement since Sept. 27. He said his father took him out of high school to home-school him.
The Star said the boy told investigators his father routinely woke him up at 4 a.m., allowed him to use the bathroom and fed him a packet of instant oatmeal. He would then be locked up until his father got back from work about 2:30 p.m. when he would get another bathroom break and a packet of ramen noodles before being restrained again, the newspaper said.
He said his supper would be a couple of baloney sandwiches with a cup of water.
The officers said the boy's father and stepmother allegedly said they restrained the boy for their safety and his after he had hit the stepmother in anger multiple times, the Star said.