One holding cell in the Xenos Bestiarium, on Watch Fortress Erioch, is apparently empty, supposedly occupied by an undetectable Tyranid organism of unknown type. The alleged occupant was caught in a stasis trap laid by a Kill-team investigating suspicious disappearances on the planet Jove's Descent in 814.M41. The trap registered something entering it but the Kill-team could detect no creature inside. As they were unable to find fault with the machine spirit of the device, the Kill-team transferred it, unopened, to the Xenos Bestiarium for further study.
The creature is believed to be some form of the Lictor or Genestealer genus with exceptional chameleon-like powers. Some believe the powers must be psionic in origin, somehow preventing the human mind from registering the xenos presence even indirectly through augurs and sensors. Another possibility is that the creature has somehow evolved an ability to shift out of phase with its environment, though this thesis raises the disturbing possibility that the being could also walk through walls. The stasis trap was allowed to fail of its own accord and whatever was held inside has so far failed to breach the containment of its holding cell.
Autosense-directed weaponry has been deployed so that in the event of an escape the entity will be cut down even if personnel fail to recognize that it has gotten free. Several options are being considered on how to deal with the xeno, including bombarding the entire holding cell with hard radiation in an effort to kill the beast, in the hopes its powers cease functioning after death. Several Battle-Brothers have also volunteered to bait the xenos into attacking them so that it can be studied. The Chamber of Vigilance is still weighing its options on the fate of the xenos, unwilling to take action while so little is known but needing to take action to find out more about this disturbing and unique new xenoform.