Baljeet Singh, who worked at the Deen Dayal Upadhyay Hospital here, was allegedly stabbed and shot dead in his house by two motorcycle-borne assailants in outer Delhi's Kanjhawala area on October 8.
The apprehended juvenile is the son of victim Baljeet's sister Snehlata, who had told police that two unidentified men barged into the house and killed her brother.
Snehlata had been living with her brother after she had separated from her husband and DTC bus driver Ajit Singh over domestic violence.
During investigation, the juvenile told police that his father remained in depression due to the complaints filed by Snehlata. He told that he paid money to two associates Rakesh and Himanshu for the murder of Baljeet, they said.
Rakesh and Himanshu are still absconding.