The three boys were abducted from Dimapur on July 28 and killed on August three at a place between Diphu and Lumding in Assam, Special Branch DSP Israel Xuivi said today.
They then telephoned the father of one of the victims, a student of class VIII, seeking ransom and were arrested yesterday when they came to collect the money at the Dimapur railway station, Xuivi said.
Of the three, two were from Karimganj in south Assam and the other from Bihar and were staying at Dimapur, he said.
The three also admitted involvement in a number of kidnaps and killings in the commercial town in the past for ransom, the DSP said.