dangerous offender

noun

US and Canadian an offender who is deemed by a court of law to be likely to engage in further violent conduct, and who thus becomes eligible for an indefinite prison sentence

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012