Masood (38) was shot dead in her car outside her residence in Bhopal on August 16, 2011 when she was about to leave for an anti-corruption rally.
Zahida Pervez, Masood's interior designer-friend, and four others, including three shooters, have been named accused in the case by the CBI.
The official, D S Badkul, told CBI court judge Anupam Srivastava that he found changes at the crime scene. Masood's body was shifted from the driver's seat to adjacent seat.
Badkul was crossed-examined by Sunil Srivastava, counsel for Saba Farooqui, Zahida's friend and one of the accused.
To a question by Srivastava, Badkul said only arms experts can say what kind of firearm, a country-made revolver or a licenced pistol - was used in the crime.
The prosecution witness was also cross-examined by Zahida's counsel A J Bhojwani, and Pervez Alam, advocate for alleged shooters Saquib Danger and Tabish Khan.
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Earlier, the medico-legal official was examined by senior public prosecutor Hemant Shukla.
Second prosecution witness Shivcharan Sharma, a government photographer, failed to appear in the court today.
The trial will resume on November 26, when two more prosecution witnesses S K Singh and B K Mahapatra, besides Sharma, would depose.
All five accused, who were present in the court today, have been charged with murder and criminal conspiracy.