Pradeep, who was named by first accused Manoj Kumar, was apprehended from Barahiya village in Bihar's Lakhisarai late last night, Bihar Director General of Police Abhayanand said.
A Delhi Police team with the help of Bihar Police Special Task Force arrested Pradeep from his maternal uncle's residence, wehere he was hiding, the DGP said.
"He will be brought to the national capital today after getting a transit remand from Darbhanga court," Delhi Police Commissioner Neeraj Kumar told PTI.
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.
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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.
Sources said Manoj told his interrogators that on April 15, his friend Pradeep had come to his house and they had consumed alcohol.
He had also claimed that they fled from the house after strangulating her to avoid being identified later and thought that she was dead, they said.
The girl is currently undergoing treatment at AIIMS here and doctors said her condition is stable. Her condition is gradually improving and she is expected to be discharged after two weeks, they said.