The accused, Shubham, was held today outside Delhi, and is being brought here, said a senior police officer.
Shubham had allegedly shot the girl in a fit of rage, police said.
They had been conducting raids at his possible hideouts across Haryana.
The girl had accompanied Shubham and Yogesh for lunch to Rajouri Garden on December 20. Shubham and the girl were sitting in the car while Yogesh had stepped out when Shubham had allegedly shot her with Yogesh's licensed pistol.
After her mother got to know about it, she had called Nitin to her house and the latter's presence had allegedly enraged Shubham who shot the victim, police had said.
Police will interrogate him to ascertain the reason behind the murder.