The three, who were detained last night, have a criminal background and are being interrogated about the killing of Rajdeo Ranjan, Superintendent of Police Saurabh Kumar Sah told PTI.
Sah said preliminary probe suggested that the killers were disturbed by the news stories of Ranjan, who was the Siwan district Bureau Chief of Hindi newspaper 'Hindustan'.
CCTV footage and mobile phone of the journalist were being checked to gather clues about the murder which took place on the busy Station Road around 8 PM last night.
Ranjan (45) was cremated today.
He is survived by his wife, who is a school teacher and a son and a daughter, who are both students.
Siwan district journalists today held a condolence meeting and demanded immediate arrest of the killers and compensation for the journalist's family.
The killing drew sharp condemnation from politicians. Chief Minister Nitish Kumar condemned the killing and ordered prompt action against the murderers.
RJD Vice-President and former Union Minister Raghubansh Prasad Singh strongly condemned the murder and sought capital punishment for those responsible.
"Its not only murder of one journalist but an attack on democracy. Killers of the scribe should be nabbed immediately and should be given capital punishment," he said.
Singh, known for his frank opinions which sometimes do not go down well with the Grand Secular Alliance of which his party RJD is a constituent, expressed concern over the law and order situation and urged to make it a top priority.
Leader of Opposition Prem Kumar visited the family of the victim.
Senior BJP leader Sushil Kumar Modi and state BJP President Mangal Pandey attended the condolence meeting in memory of the scribe.