Ludhiana, Oct. 17 (PTI): Investigators today found a flattened pencil cell inside a local theatre where a blast killed six persons on Sunday, suggesting a timer was used to set off the explosion.

Forensic tests have confirmed the use of about 500gm RDX for the blast in the Shingar multiplex hall, sources said. The tests also concluded that ammonium nitrate and calcium sulphate were not used, they added.