As a houseful of people watched, a woman stabbed and killed BJP MLA from Purnia, Raj Kishore Keshri (51), with a 12-inch kitchen knife during his janta durbar here on Tuesday.
Rupam Pathak (45), a teacher, had earlier accused Keshri and one of his colleagues of sexually assaulting her for over two years.
After the attack, she tried to escape but was caught by a guard and then beaten up by an enraged crowd. She was rescued and hospitalised by the police. She is said to be in critical condition.
Pathak had filed a police complaint against Keshri in May 2009 but withdrew it in June 2010, before the assembly elections. The MLA had dismissed her allegations as a "political conspiracy".
Later, the two seemed to have settled their differences as Keshri had inaugurated Pathak's school, built a road for it and even helped her secure a power line, sources said.
A profusely bleeding Keshri was taken to the district hospital, where he was declared brought dead. Doctors said he was stabbed twice - the first wound was below the rib cage and non-fatal but the second punctured his spleen, killing him instantly.
Chief minister Nitish Kumar ordered a high-level probe and appealed to supporters of Keshri to maintain peace even as he assured them that the guilty would be punished. He also ordered a review of the security of all legislators and made frisking of all their visitors mandatory.
Keshri, who won four successive terms, is survived by his wife and two sons.
Pathak, who was his neighbour, is separated from her husband and has two children.
Witnesses said that Pathak entered the MLA's residence at around 8am, when he was receiving petitions from his constituents, and asked to speak with him alone on a private matter. The two then had an altercation and she pulled out the knife from under her shawl and stabbed him.
Doctors attending to Pathak said she had suffered many internal injuries from the beating.