With the surrender of Gujarat police officer Dr N K Amin, state CID hopes that it could know exactly how Kauser Bi, wife of fake encounter victim Sohrabuddin, was killed in Ahmedabad in 2005.

Amin, a deputy superintendent with the CID (Crime) was wanted specifically in connection with Kauser Bi's murder.

The investigating agency had already arrested three senior Indian Police Service officers and 10 other junior officials of Gujarat and Rajasthan police who were part of the operation.

"Amin's interrogation is crucial to ascertain how the policemen killed Kauser Bi. It is known that her body was brought to the river bed at Ilol (in Sabarkantha district) by Amin and another official and cremated there," an investigating officer of the CID (crime) told PTI.

The CID will on August 23 file a fresh application in an Ahmedabad court to seek Amin's remand, who will be in judicial custody till then.

The probe agency has gathered evidence that Kauser was kept in a farm house on the outskirts of Gandhinagar along with her husband Sohrabuddin and she was shifted to another one after the wee-hour encounter in November 2005, the official said.