If I have a tenant has no lease who is behind in rent, involved in gang activity and has complaints from other tenants, how do I get him out ASAP?

The only way to get rid of a tenant is by eviction. If the tenant has unpaid rent, you can immediately file an action for eviction based on nonpayment. The weakness with that is that if he comes up with the rent by or before the court date, he can stay; therefore, as a back-up, you should simultaneously serve him with a 30-day notice terminating his tenancy, since when there is no written lease, the tenant is a month-to-month tenant on an oral lease. That way, even if he pays the rent, you'll be able to evict him after the 30 days are up, by filing a holdover eviction action.