Police hunting for the killers of 26 people in a college residence in northeast Nigeria said they had raided houses and made a number of arrests on Wednesday.
The attackers went from room to room in the building in the town of Mubi, in remote Adamawa state, on Tuesday morning and killed the people they found there with guns and machetes.
Adamawa state, like much of the north, has been targeted by Islamist insurgents, but police said were also investigating whether the killings were the result of a feud inside the college.
The police commissioner for Adamawa state Mohammed Ibrahim told Reuters by telephone his officers had made a number of arrests, but declined to give any further details.
He said the force was still keeping an open mind on whether the killings were carried out by militants or rival students, but there were signs of an "inside job".
"Relatives of the slain students said the assailants called their names out before killing them. The majority were killed with gun shots or slaughtered like goats," he added.
One possibility was that the killings were related to a dispute between rival political groups at the Federal Polytechnic Mubi following a student union election on Sunday, Ibrahim said.
"The second day after the election winners were declared, you have the killings ... Really we cannot rule out possibility that the attacks may have been carried out by either the Boko Haram or a ... gang," he added.
Boko Haram, which is fighting to carve out an Islamic state in the north of the country, usually targets politicians or security forces but has also attacked students. Security sources say it has cells in Adamawa.
Nigeria's Senate on Wednesday, in a rare resolution on the country's violence, called for a speedy arrest of the perpetrators.
"The Senate does condemn in strongest terms the killing of innocent students ... we urge the Federal Government to expeditiously apprehend the perpetrators of this act," it said.
In the northern city of Zaria on Tuesday, security forces arrested 21 Boko Haram suspects, part of an ongoing crackdown against the Islamist sect, army spokesman Captain Ibrahim Abdullahi said by telephone.