The police also recovered 20 kg of gunpowder, one 9 mm pistol, 25 rounds of live ammunition, ULFA documents, mobile phones and other "incriminating materials" from their rented accommodation at Panjabari locality in the city, Guwahati Police Commissioner Deepak Kumar told reporters here.
"We have arrested Pranmoy Rajguru, who is a pro-talk faction ULFA militant. He was acting as a sleeper cell of the outfit and was responsible for arranging all the logistics," he said.
At least 12 people, including two SSB personnel and a woman, were injured in the grenade blast in front of a shopping mall in the heart of the city on Wednesday evening.
Rajguru, Kumar said, had joined the militant group in 1986 and is a senior cadre of the outfit.
"The woman, identified as author and actress Jahnabi Saikia, was his accomplice in the crime. The house was rented by her and they moved there on May 1. They keep changing their locations," the police commissioner said.
Kumar said both of them have confessed to their involvement in the grenade blast.
He added that the police have identified two-three more people for their role in the crime and investigation is underway to nab them.
"No one involved in this bomb blast will be able to escape. They will be arrested and punished. Strict instructions have been issued to the DGP in this regard," Assam Chief Minister Sarbananda Sonowal said on Thursday.
Kumar had Wednesday told PTI that two people riding a motorcycle hurled the grenade in front of the shopping mall located at arterial R G Baruah Road, just opposite the state zoo around 8 pm.
Visiting the spot, DGP Kuladhar Saikia had said that a police barricade was set up in front of the mall to conduct routine checks of vehicles, and it is suspected the grenade was hurled aiming the police party.
The Sashastra Seema Bal (SSB) jawans were on patrolling duty with Assam Police personnel near the barricade.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)