A local court Tuesday acquitted Mridul Phukan, a surrendered militant, citing lack of evidence.

Rights groups reacted angrily saying the CBI's callous attitude in investigating the case helped Phukan go scot free.

'The 12-hour strike is called in protest against the way the CBI investigated the case. With many witnesses identifying the accused of killing Das in broad daylight, yet the CBI failed to establish the charges,' MASS leader Lachit Bordoloi said.

Several political parties, students' groups and other social organisations supported the general strike.