Muvattupuzha Vigilance Court, acting on a complaint by an activist, A.A. Paulose, asked the department to complete the probe and submit its report by November 28.
Besides Mohanlal, the roles of then Forest Minister Thiruvanchoor Radhakrishnan and three other persons will also be probed.
The case first surfaced in 2011 following an income tax raid at the actor’s house here when it came to light that he possessed elephant tusks.
Forest Department officials registered a case against Mohanlal and two others in 2012, filing the first information report (FIR) before chief judicial magistrate at Perumbavoor, naming the actor as the first accused.
Mohanlal maintained that he had purchased the tusks and then Chief Minister Oommen Chandy of the United Democratic Front (UDF) government asked Forest Minister Radhakrishnan to look into the matter.
According to rules, possession of elephant tusks by anyone is against the Forest and Wildlife Act.
The petitioner said the forest officials had erred in their duty and did not act according to the law.