The bombing was the deadliest in a decade to hit Peshawar.
Police said the attacker appeared to have passed through several barricades manned by security forces to get into the 'Red Zone' compound that houses police and counter-terrorism offices in the volatile northwestern city of Peshawar.
Purohit and six others, including BJP MP Prgaya Singh Thakur, are facing trial in the case of the blast that killed six people and left more than 100 injured in September 2008. All the accused are currently out on bail.
The blast in the Jindal Poly Films factory, located in Mundhegaon along the Mumbai-Agra highway in Igatpuri taluka, was so strong that it was heard in nearby villages.
The incident took place in the Bhupatinagar area, only 1.5 km from Contai town where TMC national general secretary Abhishek Banerjee is scheduled to address a public meeting on Saturday, a police officer said.
Police had called it an act of terrorism, invoking a stringent provision of the Unlawful Activities (Prevention) Act (UAPA), and held the passenger, Shariq, responsible for the incident.
The investigation team got information that Shariq had used satellite phones and had visited a few other towns in Karnataka and Tamil Nadu.
The NIA has also initiated proceedings to question the accused in the case.
The meeting has been called to assess security and discuss precautions in the wake of blasts in Coimbatore and Mangaluru.
The incident occurred on the popular Istiklal Street in Beyoglu.