Jail records show David McCoy, 28, was charged on Friday with capital murder of a person in a vehicle and is being held without bond.
The Huntsville Police Department did not immediately respond to inquiries from Fox News. McCoy is on administrative leave from the force.
Authorities arrested the officer over his involvement in the shooting that occurred on Lawsons Ridge Drive while he was off-duty, FOX 54 in Huntsville reported.
Sources told the outlet that McCoy shot his girlfriend in the head and then called police to report the death, apparently telling authorities she shot herself.
The sources also said the female victim, who has yet to be identified, had just told McCoy that she was pregnant, according to WAAY 31.
The Alabama Law Enforcement Agency’s State Bureau of Investigation (SBI) is taking over the investigation after Huntsville police initially question McCoy after the Friday shooting, the outlet reported.