Lieutenant Neiss was the middle-of-the-road staple of UnityPoliceForce's middle mannagement. He's not particularly heroic, racist, clever or corrupt. He was first encountered in DeadInTheWater, where TheCharacters managed to make a poor first impression.
Oh, and strictly speaking, it's spelt Neiß, but he tends to use Neiss to avoid confusing UniformedOfficers and filing systems.
Lt Neiss was assigned the investigation of MarkStein's house at the end of DeadInTheWater, and learnt from Stein's notes how to make a GrimHealingPaste from the parts of TheHellmaid. He also discovered Lloyd McDonall's involvement in the deaths of a number of young girls.
During AndTheRockCriedOut Neiss' investigation came to the notice of LewisBrown, a corrupt Detective Sergeant in the pay of TheMob. Lewis stole his notes, and used them to blackmail Lloyd into following Mob orders. When Neiss refused to go along with the scam, Brown forced Neiss out of the police HQ, in a gunbattle in which Neiss was wounded.
Neiss holed up in a porta-cabin at the back of the abandoned MolassesFactory, and used the GrimHealingPaste to recover, and start a vigilante campaign against Brown. Neiss and his team were injured multiple times during the campaign, and Neiss used the paste and parts reclaimed from murdered victims to keep his team running.
At the end of AndTheRockCriedOut, the party convinced Neiss that TheHellmaid was hiding out in Lloyd McDonall's house, and then sent Brown their after him. There was a gunfight, in which Brown was killed and Lloyd was injured, but Neiss' body was never found.