http://nakedsecurity.sophos.com/2010/12/09/are-ddos-distributed-denial-of-service-attacks-against-the-law/
DBX claims to be in the USA as I recall... that is one of the 3 example countries that will prosecute DDOS attackers. UK and Sweden being the others, and are they the only countries that prosecute cyber crimes? No they aren't.
But he can't do it anyway so whatevs.
Don't forget that CoinHunter explicitely asked to BitcoinExpress to ruin his network (like if he wasn't talented enough to ruin his own currency alone).
That's sufficient to warrant any further actions in this direction.
Also, there cannot be charges of denial of service where there is no service...
Unless you use DDoS as in Distributed Denial of Scam?