Because of the semi-anonymous nature of Bitcoin, its used in ransomware attacks. Hackers breach networks and hold them hostage until payment is made to them. Hospitals and schools have been victims of these types of attacks. However, unlike cash, which was favored by thieves in the past, Bitcoin always leaves a trail in the blockchain that investigators can follow.
This is the major problem with anonymity. There was a kidnapping in South Africa recently and I heard the criminals demanded to be paid in Bitcoin before releasing the victim is released. I think if the trail can be traced on blockchain it will be a good way to nab miscreants.