Continuity mistake: Mr Freeze's ship just appears out of the clear blue rather than having been anchored all night when you can play "In from the Cold."
Continuity mistake: Nora's cryo chamber changes in appearance in the three games it's in. 1. Arkham Origins DLC: Cold, Cold Heart. It looks like a big tube. 2. Arkham City Side Mission: Heart of Ice. It looks like a cabinet. 3. Arkham Knight DLC: In From the Cold. It's a tube again, like in Origins, but smaller.
Other mistake: If you have subtitles on while playing the DLC, In From The Cold, one militia member says the word "that" regarding Nora's cryo chamber. Yet the subtitle uses the word "the" instead.
Continuity mistake: In Batman: Arkham Origins DLC "Cold, Cold Heart," Nora Fries is wearing a long silver dress with her brown hair down at full length. Yet in the DLC "In From The Cold," she's wearing a short purple/dark blue dress with a bow around her waist, and her hair's now light brown and pinned back.
Answer: He might have used his disguised dollotrons to place the bodies or simply disguised himself when sneaking out. As Gotham is in a criminal turmoil and most of the streets are dark and empty, it wouldn't be that hard to move around in the shady alleys unnoticed. And why did he do this? Simply because he's insane. An obsessed, maniac psycho-and sociopath, also schizophrenic beyond saving. Placing the bodies on display like that is part of his "artwork," presumably showing the world how imperfect those ones were in his eyes.
Dangar