I believe Bitcoin transactions via online wallets could prevent crime. People are going to use Bitcoin for legal and illegal transactions, however criminal transactions are susceptible to crime as cash is used for the transaction...which encourages theft. If bitcoin were used for these shady transactions, perhaps with escrow, there would be no opportunity to steal currency - couldn't this prevent crime? (Aside from the original criminal transaction of course!)
No it can't prevent any crime at all, That's the reason why other country before they banned bitcoin for thinking that might gonna be use for crime or money laundering. That's all I know about it.