Investigators say gun evidence links a Colorado parolee fatally shot in Texas with the death of Colorado’s corrections’ chief.

The El Paso County sheriff’s office said Monday that “unique and often microscopic markings” found on shell casings in Texas and Colorado leads investigators to conclude that the gun Evan Ebel shot at officers in Texas was the same gun used to kill Tom Clements at his home on Tuesday.

Investigators say they don’t have a motive. They say determining that “could be a lengthy process for investigators.”