The 23-year-old victim's male friend, an engineer in a software company. identified Mukesh during TIP, a senior police official said.
Eleven people were paraded before the victim's friend during TIP which started at 3:05 PM and ended in a hour. "The procedures ended by 4 PM," the official said.
Out of the four accused, only Mukesh had agreed to TIP when he was produced before a court here yesterday. Other accused -- Ram Singh, Pawan and Vinay -- had refused to undergo TIP.
According to the official, the positive identification of Mukesh by the friend, who was also beaten up by the gang before the men allegedly raped the girl, is a shot in the arm of the prosecution as it would it them nail the other culprits.
Police have invoked the stringent charges of attempt to murder and destruction of evidence against the accused.
Investigators had earlier pressed charges against them under sections 365 (kidnapping or abducting), 376 (2)(g) (gang rape), 377 (unnatural offences), 394 (hurting in committing robbery) and 34 (common intention) of IPC.
Police have so far arrested four persons in connection with the incident in a moving bus here on Sunday night.
Investigators have also detained one person from Bihar in connection with the case though there was no official confirmation regarding that.
Sources said one more accused is to be nabbed and police teams are searching for him.
Police have sent teams to Bihar, Rajasthan, Uttar Pradesh and Haryana to trace the absconding accused.