A Natrona County District judge sentenced a Casper teenager on Thursday to 12 to 20 years in prison for participating in a string of armed robberies last fall.

Kasey Conrad Miller, 19, had previously admitted to robbing three Casper convenience stores at gunpoint in October. He also burglarized a pawn shop in September and tried to rob another one in November.

In June, Miller pleaded guilty to three counts of aggravated robbery and one count each of attempted aggravated robbery and aggravated burglary. He, along with two other men, was arrested in November following the armed robbery of a convenience store in Laramie.

Investigators were later able to tie all three men to the Casper heists.

Miller was sentenced in June to six to 12 years in prison in connection to Laramie holdup, said Assistant Natrona County District Attorney Michael Schafer. Miller will be allowed to serve both sentences at the same time.

All three men -- Miller, 21-year-old Aren Patrick Cobia and 20-year-old Skylor Eberhardt -- made plea agreements with prosecutors. Cobia and Eberhardt have not been sentenced for the Casper robberies.

Eberhardt and Miller broke into the Depend-A-Pawn shop in September and stole weapons, then robbed convenience stores three times the following month. Cobia participated in one of those robberies.

All three men tried to rob the United Pawn shop in November, but fled after they heard the store's alarm had been activated.

Reach crime reporter Joshua Wolfson at (307) 266-0582 or at josh.wolfson@trib.com.