Pradeep, the second accused, was apprehended from Bihar in a joint operation by Delhi and Bihar Police, Delhi Police Commissioner Neeraj Kumar told PTI.
"He will be brought to Delhi today after getting a transit remand from Darbhanga court," Kumar said.
Manoj, the first accused who was arrested on Saturday from Muzaffarpur in Bihar, had told police during interrogation that one of his friends was also involved in the crime.
The girl was raped on April 15 in a building in east Delhi's Gandhinagar locality where the victim and accused Manoj lived and she was rescued 40 hours later on April 17.
Manoj had fled from the house thinking that the girl was dead.
Pradeep's arrest came after investigators yesterday launched a hunt following protests here demanding the removal of the Police Commissioner.