Unidentified persons attacked a CPI(M) worker at Kalleri near Vadakara at around 1 am on Tuesday and set his car on fire. The CPI(M) worker has been identified as Onthammal Biju. Vadakara police have registered a case and started investigation. Biju was earlier accused of helping Arjun Ayanki, an accused in the Karipur gold smuggling case. Police suspect that the incident is related to smuggling of gold. Political reasons are also suspected.