The Delhi Police on Wednesday filed a petition in the supreme court challenging the acquittal of suspended IPS officer Ravi Kant Sharma and others in journalist Shivani Bhatnagar murder case.

The police has filed the appeal against the October 12, 2011 verdict of the Delhi high court acquitting R K Sharma and two others by giving them benefit of doubt.

The high court had only upheld the conviction of Pradeep Sharma, one of the four persons, found guilty by the trial court.Besides R K Sharma, others acquitted by the high court were Sri Bhawgan and Satya Prakash.

The high court had said although the motive behind the killing of the Indian Express scribe was unclear, it raised questions whether Pradeep Sharma acted alone or at the behest of R K Sharma and others or at the instance of someone else.

"These are questions which we cannot answer on the basis of the material before us. The quality of evidence before us is not of a high calibre," the high court had said, adding that the call records, the key document, is riddled with so many problems that it cannot be relied upon.

The high court bench of justices B D Ahmed and Manmohan Singh had said the prosecution has failed to establish the link between R K Sharma and the killer and even the crucial records relating to the call details were tampered with and cannot be relied upon.

It said the prosecution failed to prove the motive behind the offence and the link between three co-accused, who were acquitted, and Pradeep Sharma, the man who killed the victim in her East Delhi flat on January 23 in 1999.

The high court had rejected the plea of the prosecution that Shivani was eliminated at the instance of R K Sharma, then director vigilance of Air India, as he wanted to get out of their "full-blown love affair".

The scribe had threatened RK Sharma that she will expose him, the prosecutor had alleged, adding it amply established the motive behind the murder which has also been supported by the call details of Shivani's landline phone and the mobile phone of the IPS officer.

The police cited the statement of witness Saijal Shah that R K Sharma, when he was the OSD at the PMO, had visited Shivani in London where she was pursuing a course.

The scribe was in possession of certain classified documents and had threatened the IPS officer to expose him by making them public, the prosecutor had alleged.

The lukewarm response of the IPS officer on the birth of Shivani's child allegedly irked her and she threatened to ruin the life and career of Sharma. As a result, he hatched the conspiracy to kill her, the prosecution had alleged.