He began a series of treason trials and executions, which continued until his death in 37.[25] He left power in the hands of the commander of the guard, Lucius Aelius Sejanus. Tiberius himself retired to live at his villa on the island of Capri in 26, leaving administration in the hands of Sejanus, who carried on the persecutions with contentment. Sejanus also began to consolidate his own power; in 31 he was named co-consul with Tiberius and married Livilla, the emperor's niece.