was commander of the night-watch (praefectus vigilum) in the 18th year of the reign of Tiberius, A. D. 31. When the emperor had commissioned Sertorius Macro to arrest Sejanus, Laco was stationed with his band of vigiles around the temple of Apollo, in which the senate was held. At a preconcerted signal, after Tiberius' letter (Juv. Sat. 10.71) had been read, Laco entered with his guards and took Sejanus into custody. For this service, which from the power of the criminal required both secrecy and boldness, Laco was rewarded with a large pecuniary donation and with the quaestorian ornaments. (D. C. 58.9, 10, 12.)
[W.B.D]A Dictionary of Greek and Roman biography and mythology
Smith, William
A Dictionary of Greek and Roman biography and mythology. William Smith, LLD, ed. 1890