However, police have refused to disclose the identity of the detained person.
Delhi Police had on December 18 arrested the driver of the chartered bus, in which the assault took place, his brother and two more people
While Ram Singh, the driver of the bus, Vinay Sharma, an assistant gym instructor and Pawan Gupta, a fruit seller, were arrested from the capital, Singh's brother Mukhesh was nabbed from Rajasthan.
The bus driver along with six others had allegedly gang raped the para-medical student on Sunday night.
The victim is in a critical condition in the Safdarjung Hospital here.
Yesterday, one of the four accused was "identified" by the victim's friend during a Test Identification Parade (TIP) at Tihar jail here.
Delhi Police will today submit its status report in the High Court on its investigations in the case.
