The incident occurred during the wee hours at Shivbachan Chowk in Saran, when a team of police and administrative officials stopped the RJD cavalcade for election related checking, police said.
Prasad and his wife Rabri Devi, both opposed this on the grounds of "non-availability" of women police personnel and search order papers.
The atmosphere was vitiated with frayed tempers and exchange of angry words, police said.
A large crowd of RJD supporters also assembled around. An empty black SUV present on the spot and without a hind number plate added to the drama.
"Eight criminals were following us in this black SUV since we started from Chhapra. The plan was either to kill us or to implant cash in our vehicles. When they could not overtake us, the police stopped us on the pretext of search without any women constable or proper permission papers," said Prasad.
"This black SUV was following us for a long time. This is a conspiracy to kill us. The police had checked our vehicle and suitcase earlier also so there was no reason for checking again," Rabri said.
After a heated exchange of words, Prasad lost his temper and lambasted all the government officials present there, who beat a hasty retreat.
Rabri went to Sonepur police station to file a case alleging threat to her life. The policemen there have accepted her complaint, but are yet to register an FIR.
"This was a conspiracy by the communal forces to stop us. This was done intentionally. There was no videographer with the police. They tried to harass a woman candidate. I am not letting this go. We will be complaining to the EC today itself," Prasad said.