Rogelio Martinez was found severely injured at the bottom of a 14-foot culvert near Van Horn in November.
He was taken to the hospital where he died.
The autopsy shows he had a fractured skull, a brain injury, a broken collar bone and several broken ribs.
However, the medical examiner couldn't figure out how he got those injuries, if he was murdered or if it was an accident.
Martinez's partner was also injured but survived. He said he can't remember what happened that day.
RELATED: Fallen Border agent remembered as 'good guy' who wanted to 'make a difference'