Authorities estimate the boy's age at 3 months to 1 year and that his body was in the attic five or six years.
The Amarillo Globe-News reports Friday that police are questioning a man in connection with the case.
Officers suspect the boy was Miguel Nunez, born in 2003 and missing since 2004. Nunez' family lived in the house about the time he disappeared.
A preliminary autopsy failed to identify the body and cause of death. DNA and other tests will be done.