A 13-year-old Colorado boy suspected of shooting his father dead and concealing the killing for days by calling the man's work to say his dad was sick made his first court appearance on Monday as prosecutors weighed whether to charge him as an adult.

Kai Kelly was arrested last week on suspicion of first-degree murder in the death of his father, Joseph Kelly, in the small mountain town of Gypsum, about 105 miles (170 km) west of Denver.

Jill Sarmo, spokeswoman for the Eagle County District Attorney's Office, said the boy was appointed a public defender on Monday and will be formally charged at a later date. She said prosecutors have not decided whether to charge him as an adult.

Police uncovered the crime after the boy called his father's employer several days in a row to say his dad was sick and would not be coming to work, according to a statement from Eagle County Sheriff Joe Hoy.

The employer ultimately became suspicious and contacted police. When deputies arrived at the home, Kai Kelly told them his 50-year-old father was dead inside, police said.

The elder Kelly died from two gunshot wounds to the head fired from a .22-caliber rifle, Eagle County coroner Kara Bettis said.

"One (shot) was to the back of the head and one to the temple," Bettis told reporters, adding that the shot to the temple was a "contact" wound.

Based on the condition of the decomposing body, it appeared that the man had been dead for six days, Bettis said.

Authorities have not released a possible motive for the slaying but said Kai Kelly was under investigation for spray painting graffiti, and Joseph Kelly had failed to show for a meeting with police about the incident.

The sheriff said the boy's parents are divorced, but did not provide other details about the mother. - Reuters