The Sovereign Order of the Count of Monte Cristo is a well-hidden group of individuals. They came to Earth many years ago. The plan was to take over and end the human race. But upon analysis of the beings they realized humans weren't a threat in any way. They decided to just co-exist. Beside the humans made excellent comic relief.
It just happened now was one of those comedic moments. Apparently the government is experimenting on cadavers trying some new reanimation and stem cell procedures. The Sovereign Order of Monte Cristo had seen all this go down in the last place they resided. They just couldn't believe the stupidity, so they watched and with a snicker. One day it happened. The cadaver twitched.
Before anything could be done the cadaver was fully reanimated and had already killed the doctor and two nurses. The guards tried to contain it. But while they focused on the undead cadaver the doctor and two nurses had full reanimated and lunged at them.
The Sovereign Order of Monte Cristo decided to step in before it got out of control. The cadaver, the doctor, two nurses were chasing another guard. They had to give it to that guard he ran like the wind. The dead can't talk we all knew that, but they could communicate telepathically. When the Order linked into their mind they could hear their words as if spoken out loud.
Apparently the dead do not like being prodded and poked. And they certainly don't like being awoken from a dead sleep. It pisses them off. The doctor, guard and nurses were pissed because they got killed. So the Sovereign Order of Monte Cristo told the undead they would give them all a proper burial and a make sure they were not disturbed.
If this had gone any further that would have been the beginning of the end of the human race. This is how the Sovereign Order of Monte Cristo stopped the zombie apocalypse.