According to information to Iltalehti, the man who previously went by the name Juha Valjakkala was found dead on Monday evening.
It is currently unclear what the cause of death is.
The man was sentenced to life imprisonment for the well-known Åmsele murders of a family in Västerbotten in 1988. Then he went by the name Juha Valjakkala.
Since then, he has escaped from prisons repeatedly, most recently in October last year.