A man from the rural eastern Arizona town of Springerville already being held on a murder charge pleaded guilty to that murder and two other previously undisclosed killings on Wednesday.

Apache County Attorney Michael Whiting says 21-year-old William Inmon told authorities he would have continued his killing spree if he had not been caught.

Inmon was among four people charged in the death of a 16-year-old boy from nearby St. Johns. Authorities say Inmon previously had been considered a potential suspect in another murder.

Wednesday's guilty pleas on the second and third murders came as a surprise.

Whiting said Inmon confessed to the shooting deaths of 60-year-old Daniel Achten, who had been missing for five months, and 72-year-old William "Stoney" McCarragher, whose 2007 murder was unsolved.