Violent crime is defined as a crime in which violence is perpetuated or threatened against the victim. It is important to note that the threat of violence is enough to constitute violence.
Examples of violent crime are murder, rape, and assault, to name just a few. A crime like robbery could be violent or non-violent, depending on the circumstances. For example, if somebody broke into your home and robbed you while you were out of town, it would be a non-violent robbery. However, if someone came to rob your home while you were there, and beat you up or held you at gunpoint (even without shooting), then that constitutes a violent crime.
The prior record of a criminal has no bearing on whether or not a crime is violent. If a first-time perpetrator holds a family up at gunpoint, it still constitutes a violent crime.