For years police and banking-industry sleuths doubted they’d ever catch the phantoms behind Carbanak. Then, in March, the Spanish National Police arrested Ukrainian citizen Denis Katana in the Mediterranean port city of Alicante. The authorities have held him since then on suspicion of being the brains of the operation. Katana’s lawyer, Jose Esteve Villaescusa, declined to comment, and his client’s alleged confederates couldn’t be reached for comment. While Katana hasn’t been charged with a crime, Spanish detectives say financial information, emails, and other data trails show he was the architect of a conspiracy that spanned three continents. And there are signs that the Carbanak gang is far from finished.