The forensic report submitted to the Special Investigation Team probing the killing of Lankesh is part of the first chargesheet filed recently by the SIT naming KT Naveen Kumar as an accused.
This is the first official confirmation of the link between the two killings which happened after a gap of two years of each other.
Kalburgi (77) was shot dead in his house on August 30, 2015, in Dharwad and 55-year old Lankesh on September 5, 2017 in Bengaluru.
The SIT members had earlier talked about the same-gun theory but for the first time it has come out in the open to show that Kalburgi's murder was the handiwork of the same gang.
The bullets in both cases "have been fired through a single country made pistol chambered for 7.65 mm caliber pistol cartridges," a source said quoting the report.
The report also pointed out that the scratches formed by the firing pin on the bullets tallied among themselves.
Lankesh, who was known for her strong anti-Hindutva stand, was shot dead in front of her house, triggering a nationwide outrage.
The SIT formed to investigate her murder has formally arrested Naveen Kumar of Maddur as one of the accused.
Four more persons have been arrested for allegedly plotting to kill another rationalist and writer K S Bhagawan, also a strong critic of Hindutva.
The SIT is also probing whether they have any links with the Gauri muder case.