Tevren was an only child, and born with telepathic ability, rather than developing it in adolescence as per usual in Betazoids. He was also brilliant, earning four university degrees before growing bored with academia.
Following university, he became a government researcher, with high clearance to the official records of Betazoid history. In the course of his work, he discovered records of a small group who, in or around the 20th century, discovered unique applications of their telepathic skills, including the ability to kill. Though the specific knowledge was destroyed and lost, Tevren was able to recreate the group's work, and killed several people -- including his parents -- before being caught by the authorities.
Tevren's crimes and arrest were kept secret from the general population, and he was incarcerated at the prison for the criminally insane at Jarkana on Darona in 2358. There, he was implanted with a psionic inhibitor, which prevented him from projecting telepathically. For four months shortly after his imprisonment, Tevren was under the care of psychiatric counselor Deanna Troi. Throughout his time in prison, he was remorseless and, despite the use of numerous therapies, made no progress toward rehabilitation.
In 2375, during the Dominion occupation of Betazed, the Betazed resistance asked Starfleet for their help in freeing Tevren and delivering him to the resistance, so he could share his lethal knowledge to the resistance. Commander Deanna Troi was recruited by Commander Elias Vaughn of Starfleet Special Operations to help retrieve Tevren. His psionic inhibitor was removed in order to help the retrieval team escape a Jem'Hadar patrol, but after seventeen years, the sudden increase in cerebral activity proved fatal. Just before dying, however, he forced his knowledge and his memories into Troi's mind. (TNG novel: The Battle of Betazed)