Eleven people were killed in a forest fire in Kurangani hills in Western Ghats on Saturday.
30-year-old Ranjith was arrested last night, they said, adding that he was being questioned to ascertain whether he had any links with a Chennai-based group which is believed to have arranged for the expedition that turned tragic.
Police are probing, among others, how the trekkers came into contact with Ranjith, a local.
The 36-member team -- 24 people from Chennai and 12 from Tirupur and Erode districts -- trekked to Kurangani hills on March 10.
The team included 25 women and three children.