Yes. Technically you only need to have one conviction as the long as the crown is able to establish that there was a pattern of violence. You can in fact tender evidence during a dangerous offender proceeding that goes outside of a conviction. In other words, you can have a number of witnesses come and testify that the individual had done a number of other violent offences even though they weren't charged or convicted. I think you will find, to my knowledge...and again, there are a couple of such dangerous offenders already. Although it is a rare circumstance, it can happen.
