Sheriff's deputies charged Castillo with Palacio's death back in Sept. after matching his DNA to the scene. Investigators found Palacio's body in a ditch along County Road 7800, west of Slaton. The 21-year-old had been strangled.
DPS revealed the investigation into Palacio's death was linked to the killing of Carbajal.
Carbajal's body was discovered in north Lubbock County in 2004. Sources then told FOX34 that she and Palacio were roommates at some point.
If convicted, Castillo faces the death penalty or life in prison without the possibility for parole. He is held on a $500,000 bond.