In 2005 he became director of the Central Antiterrorism Service and, in the July of the same year, he contributed to the arrest of Hamdi Adus Isaac, a responsible of the 21 July 2005 London bombings. Other investigations he directed were those on the mafia Via dei Georgofili Massacre and the assassination of . On 16 December 2006 he was appointed as director of SISDE, a position he held until the service was disbanded the following year and replaced by AISI. Gabrielli remained as director the latter until 15 June 2008.