Hmmm... I see that the Star Trek link doesn't work.
Ok, here's the relevant info on Redjak.
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"It has a name! Beratis, Kesla... Redjac!"
– Sybo, 2267 ("Wolf in the Fold")
Redjac (also known as Red Jack, Jack the Ripper, Beratis, and Kesla) was a non-humanoid lifeform that existed for centuries by journeying from planet to planet and feeding on the pain and fear he caused by committing mass murders. (TOS: "Wolf in the Fold")
Physiology
As a being without form, which was likened to a cloud creature, its physical appearance unknown, but it was described by Mr. Scott after a brief encounter in the dark as, "cold… like a stinking draft out of a slaughterhouse, but it wasn't really there."
Spock believed that female victims were chosen more often than male ones because "women are more easily and more deeply terrified, generating more sheer horror than the male of the species."
It was similar to a parasitic organism, and required the possession of a humanoid host in order to commit crimes. It also had the ability to possess objects, like the USS Enterprise. (TOS: "Wolf in the Fold")
History
Crimes committed under various pseudonyms:
On Earth and Mars:
19th century: several women as Jack the Ripper
1932: Seven women in Shanghai, China
1974: Five women in the city of Kiev, USSR
2105: Eight women in the Martian colonies
Outside Sol system:
2156: Ten women in Heliopolis on Alpha Eridani II
Interim: several women (as "Kesla") on Deneb II.
2266: several women (as "Beratis") on Rigel IV
2267: several women (in the form of Hengist) on Argelius II
After Redjac committed a murder on the pleasure planet Argelius II in 2267 as "Hengist", Lieutenant Commander Montgomery Scott from the Federation starship Enterprise was accused of the crime. However, Hengist's true identity was later revealed. In the process, Redjac briefly possessed Prefect Jaris, who was quickly liberated by a nerve pinch from Spock. Subsequently, the Redjac entity was beamed, on a dispersal pattern, into deep space by Spock, where it was hoped that it would die from lack of nourishment. (TOS: "Wolf in the Fold")-----------------------------------------------------------
Redjak left Kiev in 1975 and is now somewhere in the United States.
Eleven years ago he became overconfident and sloppy and the police were able to apprehend him. Or rather, they were able to apprehend the human host that this parasitic energy being was then inhabiting. Since his escape from Arkham he's left his old host body and transferred to a new and younger host.
This means that the police have little chance of catching him again. They are looking for a older man. When they finally track down this person they'll assume that they have Redjak back in custody again. But this person will have no memory of his actions after Redjak possessed him. So he'll be of no help to them.
When young women start disappearing again and their bodies start turning up in pools of deep quicksand the police will think that a copycat killer has taken over from the Redjak they are holding in their cells. Little do they know the truth!