All of the 'trustless' tumbling solutions I've seen tend to leave some evidence on the blockchain, it often only dilutes the certainty that a particular input maps to a particular output.

IMO, the only "surefire" way to launder bitcoin is traditional money laundering: send a trusted person dirty bitcoins and they send you back bitcoins from a clean legitimate source. Strong incentive for launderer to take the funds and run, so trust is unstable in this model.