[sect. 3]
idem homines: M. Brutus and C. Cassius were among the former Pompeians, whose pardon and advancement by Caesar had probably excited the envy (invidiae) of those who had followed Caesar throughout the Civil War, and these two men joined the conspiracy to kill him (exitio).
illi: i.e. Caesari.
impunite: found only once elsewhere (Cic. de Finibus, 2.59) in classical prose.
timerent: we should expect some verb like sperarent or cuperent before timerent.
libertatis auctores: Cicero repeatedly calls the conspirators liberatores, e.g. Att. 14.12.2; Phil. 1.6.