Jamieson, Fausset and Brown on Mark 14:67

67. And when she saw Peter warming himself, she looked upon him--Luke (Lu 22:56) is here more graphic; "But a certain maid beheld him as he sat by the fire"--literally, "by the light," which, shining full upon him, revealed him to the girl--"and earnestly looked upon him"--or, "fixed her gaze upon him." His demeanor and timidity, which must have attracted notice, as so generally happens, "leading," says Olshausen, "to the recognition of him."

and said, And thou also wast with Jesus of Nazareth--"with Jesus the Nazarene," or, "with Jesus of Galilee" (Mt 26:69). The sense of this is given in John's report of it (Joh 18:17), "Art not thou also one of this man's disciples?" that is, thou as well as "that other disciple," whom she knew to be one, but did not challenge, perceiving that he was a privileged person. In Luke (Lu 22:56) it is given as a remark made by the maid to one of the by-standers--"this man was also with Him." If so expressed in Peter's hearing--drawing upon him the eyes of every one that heard it (as we know it did, Mt 26:70), and compelling him to answer to it--that would explain the different forms of the report naturally enough. But in such a case this is of no real importance.