Jenna thinks something is stopping the souls of the departed from moving on.
The longer they stay, the more what is left of their humanity erodes, leaving just hunger and hatred. Those they kill are also trapped, creating more and more of them.
Looking at the distribution of the bodies, the emergency pumping station is close to the nexus.

Wargames Atlantic Zombies painted with Citadel Aethermatic Blue Contrast paint.
Inspired by Dentatus' scenarios earlier in the thread and the ghosts in Lockwood and Co.