The arrest warrant says "slightly ajar."
This claim is apparently being contradicted by a witness who has related that she heard the officer order the victim to open the door.
Even in Texas, where home owners have very large "checks" regarding self defense, summoning an identified intruder to the door, then executing him would be pushing the limit.
This officer needs to be quiet and offer to plead guilty to Manslaughter ASAP. The prosecutor has stated that he will consider additional charges if the investigation warrants them. I don't think it would take too many contradictions or implausibilities for him to file Second Degree Murder charges.