A special unit of Guwahati police nabbed Sarania and three others -- Sarfaraz Ali Nawaz, Pankaj Kalita and Pradip Choudhary -- for their alleged involvement in a dacoity.
Sarania is a senior leader of the Arabinda Rajkhowa faction of ULFA, which is currently engaged in peace talks with the Centre. Sarania joined ULFA in 1990 and at one point of time headed the dreaded 709 Battalion of the outfit, the sources said.
The four arrested persons allegedly involved in the dacoity at the house of Guwahati-based businessman Rajen Lohiya on July 30 when Rs 38 lakh in cash were looted.
It was also suspected that the dacoits killed Lahoya's employee Suresh Patil on the same day and his manager Vinit Jain on August two, but the bodies were not found yet.
Jain was also allegedly involved in the plot. But, following disagreement over share of the booty, Jain was murdered, the sources said.
The police were interrogating Sarania and his aides at the city's Panbazar police station to find out what happened to Patil and Jain.
Two other accused in the case remain at large.