Sarla Mishra, a congress woman was found dead under mysterious conditions at her residence in South TT Nagar on Feb 14, 1997.
Diggy and others have been accused of trying to hide evidence in the murder case. The TT Nagar Police closed the case after probing for three years.
However, Mahesh Garg, an ex-ward councillor filed a petition with a local court against Singh and his brother and the then station in-charge and several other police officials and doctors.
Garg appealed that the officials be directed to submit statement of all witnesses involved in the case.
The court will hear the case on Jul 28.