 He also took part in the Garda Crime and Security Branch and the Special Detective Unit.In the early 1990s, he was appointed as head of the "Tango Squad", a group of Gardai who spent the large majority of their on-duty time monitoring the activities of Martin Cahill, a notorious Irish mob boss.The Tango Squad proved to be successful in thwarting many of Cahill's activities and preventing him from taking on any major criminal objectives; this helped boost Callinan's career significantly.