The suspects are being questioned over a range of offenses, including arson, rioting, attempted murder and murder, said L.L. Doungal, the police chief of Nagaland, where the attack occurred Thursday evening.
They're alleged to be among a crowd of thousands of people who stormed a jail in the Dimapur district, and dragged out the suspected rapist before beating him to death in the street. The 35-year-old victim had been accused of raping a local woman last month.
"There were thousands of them. Many of them were students in uniform," Doungal said when news of the attack first emerged.
The dead man was initially identified as an undocumented Bangladeshi settler, but now police say they still are determining his nationality.
"I am not ruling out that he's not a Bangladeshi. I am also not denying that he is not an Indian. We are verifying his nationality," said G. Akheto Sema, an additional director-general of Nagaland's police, when asked about local reports suggesting the attacked man was an Indian citizen.
Dimapur town remains under a curfew, Sema said, amid growing tensions between native Nagas and Bangladeshi migrants in the district.
Thousands of protesters demanding the cancellation of trade permits for Bengali-speaking settlers tore into the prison complex Thursday and pulled out the suspect, Doungal said.
Police initially used teargas and bamboo canes to rescue the man, but it didn't work, he said. "There were students in uniform. So, we had to use minimum force," Doungal added.
Later, police opened fire, but it was too late to save the suspect.
Protesters had planned a public hanging, but the suspect died from injuries in the attack, according to authorities. "We retrieved his body before it could be hung," Doungal said.
With English as its official language, Nagaland is located in the extreme northeastern end of India, along the border with Myanmar.
Home to about two million people, the state is spread over 16,500 square kilometers, with a relatively high literacy rate of 67%, compared with other densely populated parts of India.
Ethnic tensions are rife in Nagaland and other provinces of the impoverished northeast region. Some local groups want greater autonomy, and there's general discontent over the alleged neglect of the region by successive central governments.