The blast had occurred near a poll campaign venue of Congress leader Harminder Singh Jassi whose daughter is married to the son of jailed Dera Sacha Sauda chief Gurmeet Ram Rahim Singh.
The police and counter-intelligence officials had yesterday produced four people, all car mechanics and painters, before a court in Talwandi Sabo near Bathinda, an official said.
They identified the car based on the repainting and other works done on it and after giving details to the case's investigating officer in Bathinda, they decided to record their statement before the magistrate, police said.
"Senior officers have been working on the case. Now, we have got important leads to reach the real culprits... These four deposed before the court in connection with the blast," Senior Superintendent of Police (SSP), Bathinda, Navin Singla said.
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Investigations revealed that the car was repainted from maroon to white, police said.
Ranveer Singh Khatra, Deputy Inspector General (DIG), Counter-Intelligence, said the probe led them to the workshop in Sirsa. The workshop's owner had closed the unit last year and opened a new one, he said.
"The owner is still at large," Khatra said.
The blast had occurred minutes after Jassi had ended his election meeting near Vishavkarma Bhawan in Maur on the January 31 night, barely days ahead of the Punjab Assembly elections.