Jurors convicted a 23-year-old man of killing a mentally impaired adult to steal his Xbox 360 gaming system.
An El Paso County judge sentenced Derek Lee Hernandez to two mandatory terms of life in prison immediately after the Colorado jury's verdict.
His co-defendant, Kyle Sebastian Stott, is already serving a life sentence after being convicted earlier.
Prosecutors said 22-year-old Jason Holley was nearly beheaded with a double-edged blade in January 2009. Authorities found his decomposed body four months later in a ravine.
The Colorado Springs Gazette reported that Mr Holley had the maturity of a child and had been diagnosed with Klinefelter's syndrome, a genetic disorder that gave him an extra X-chromosome.