Watch this video

Around the 20 second mark, you see the military shooting civilians centre mass followed up by their unit commander shooting the dead bodies once in the head with a Berretta 9mm. This was BEFORE the audience knew of people re-animating regardless of death barring severe head injury.

If The Walking Dead universe had no Zombie films then how did those soldiers know to shoot those executed hostpital workers in the head after initially gunning them down. I know i'm not alone on this in speculating that it was a secret government/military project that caused Wildfire, given that Jenner said the pandemic started in the US and didnt spread to Europe for atleast another month (can't remember specific time frame).

Also the deleated scene with regards to the fate of the Vatos, who also had the majority of their members shot in the head too, probably by the military who are still operating but hiding in underground bunkers most likely.