Some studies have shown a strong relationship between graffiti and other crimes.
Discovered via this blog post by David Eaves.
As for the two vandals arrested in Tinakori Rd last Easter. Their case was heard 8 December 2010. Both were convicted. Apparently, one had committed even more serious crime and later in 2010 was incarcerated for two years. The other graffiti vandal got 40 hours community service.