PORTLAND, Ore. – Portland police arrested a man for manslaughter and negligent homicide after his two-year-old nephew died of a methadone overdose.

Willie Lee Harris Jr., 35, was arrested by homicide detectives. A Multnomah County grand jury indicts him of four charges, including manslaughter in the second degree, tampering with physical evidence, criminal mistreatment in the first degree, and unlawful possession of heroin.

Wednesday in court, Harris pleaded "not guilty" to the charges, and reserved all rights.

On Oct. 10, detectives were called to a Portland hospital to investigate the death of 2-year-old Reginald Harris Jr.

Investigators determined the boy died of a lethal dose of methadone, which is an opioid medication used to treat pain.

“Detectives do not believe that Harris intentionally gave his nephew methadone, rather it was left in a place where the child had access to it,” said Sgt. Pete Simpson with Portland police.

Police said the case is a sad reminder to keep prescription drugs in places where children cannot find them.

Harris also faces charges of criminal mistreatment and possession of heroin, in addition to several outstanding warrants for his arrest.