Justice Ganguly was forced to resign as the West Bengal Human Rights Commission chief a few months ago after a former law intern alleged that he sexually harrassed her in December 2012.
According to the Delhi police, the woman has failed to join the probe despite repeated requests.
The material available in public domain so far is insufficient for the police to take up a case suo motu, said the police.
Justice Ganguly had denied of committing any such crime.
"I have not done anything to feel ashamed of. The allegations were made by the intern 11 months after the incident. This was organised to defame me. The West Bengal government was very uncomfortable with me as the WBHRC Chief," Justice Ganguly had said.