"The six-member NIA team visited the Jiram valley (located around 400 kms from state capital Raipur) in Darbha region of Bastar, where the attack was executed," a senior police official told PTI, on condition of anonymity.
"The security has already been stepped up in the region after the attack," the official added. The team was accompanied with the technical staff of Special Protection Group (SPG), senior officials of Central Reserve Police Force (CRPF), besides forensic experts.
The NIA team inspected the attack site for nearly two hours during which they collected blank cartridges and other material as evidence, the official said.
The team also investigated the vehicle which turned turtle after being blown up in landmine blast triggered by naxals before they opened indiscriminate firing on the convoy. They also inspected the route and its nearby locations.
The road that was damaged after the landmine blast has been repaired after the attack for connectivity in the region, the official said. There is a possibility of more visits by NIA to the site, the official added.
Heavily-armed Maoists had on Saturday ambushed a convoy of Congress leaders in the Darbha region, killing 27 people including PCC chief Patel, his son Dinesh, Congress leader Mahendra Karma and ex-MLA Uday Mudliyar and injuring 37 others, including former Union minister V C Shukla.
Home minister Sushil Kumar Shinde had on Sunday ordered a NIA probe into the attack. Chhattisgarh government has also ordered a judicial probe in the attack.