Josephus

Some Jews (first century) did believe in eternal conscious torment, according to Josephus. Josephus describes the beliefs of the Essenes as follows:
For their doctrine is this. That bodies are corruptible, and that the matter they are made of is not permanent; but that the souls are immortal, and continue for ever, and that they come out of the most subtil air, and are united to their bodies as to prisons, into which they are drawn by a certain natural inticement; but that when they are set free from the bonds of the flesh, they then, as released from a long bondage, rejoice and mount upward… good men are bettered in the conduct of their life by the hope they have of reward after their death, and whereby the vehement inclinations of bad men to vice are restrained, by the fear and expectation they are in, that although they should lie concealed in this life, they should suffer immortal punishment after their death. These are the divine doctrines of the Essenes about the soul. (Wars 2.8.11)
Likewise, according to Josephus, the Pharisees believed in eternal conscious torment:
They say that all souls are incorruptible, but that the souls of good men only are removed into other bodies, but that the souls of bad men are subject to eternal punishment [aidiō timōria]. (Wars 2.8.14)
However, the Sadducees did not believe in eternal conscious torment; in fact, they didn’t believe that there is any life after death, and that good and bad deeds are rewarded in this life only (Wars 2.8.14). Obviously the Sadducees’ view is incompatible with the soteriology of the New Testament authors, and a few of them explicitly spoke out against it (Mark 12.18-27; Acts 23.6-9).