Tribune in 44 (Dio 44.52.2), and one of the conspirators along with his brother P. Casca Longus (Cic. Phi.l. 2.27; cf. Suet. Iul. 82.1, alter e Cascis; Nic. Dam. Vit. Caes. 24, FGrH 2A.408f.; Plut. Caes. 66.5; Brut. 17.3; cf. App. BC 2.113, who names Gaius only, and Eutrop. 6.25, who mentions only one Casca; see Münzer, RE), but according to Dio (44.52), he escaped the fate of Cinna (see above) by announcing that the name Casca was all that he had in common with the conspirator. (Broughton MRR II)
p. 257-63 (Thommen 1989)
T. J. Cadoux believes that the evidence in our sources points to the existence of three rather than two Cascas, the two members of the conspiracy, and C. Casca, Tr. pl. 44, who announced his innocence by claiming that the name Casca was all that he had in common with the conspirator (Dio 44.52). Cadoux's note reads as follows: I feel that the evidence points to three Cascas: (1) the brother of Publius who shared in Caesar's murder (praenomen nowhere stated); (2) C. Casca, Tr. pl. 44, who announced his innocence of the murder; (3) P. Casca Longus, Tr. pl. 43, the prominent conspirator. Muenzer (see 53) and you unite the first two: but it was notorious that the two Cascas, brothers, were involved in the murder, and therefore only a third could have established his innocence. This naturally gave rise to confusions: thus Appian (BC 2.113) wrongly applies the praenomen Gaius to his one Casca, probably intending the more prominent Publius (it is of course possible that his brother was in fact also a Gaius, which would aid the confusion); and Dio, who knows of only one Casca among the murderers, Publius, wrongly makes him tribune of the plebs in 44 (44.52.2) as well as in 43 (46.49.1). Suetonius' words "alter a Cascis" (Iul. 82) refer to the two guilty brothers and by no means exclude a third contemporary Casca; Eutropius is simply naming the four most prominent murderers. The claim that the tribune of 44 had only the name Casca in common with the conspirators provides an important support for the distinction, and suggests that his gentilicium may not have been Servilius. Shackleton Bailey agrees that the evidence is in favor of the existence of three Cascas (Onom.). The entry in the index for this Casca would then be: C. Casca, Tr. pl. 44. (Broughton MRR III)