Udawalawa police had made the arrest on May 22, during a raid in the Belawanagala area, three weeks after the incident had taken place.
The muzzle loader gun used by the suspects to kill the calf and a stock of gunpowder were seized during the raid.
During interrogation, the suspects had admitted to killing the calf while drinking Goda in the illicit brewery run by them.
Police investigations to arrest these suspects had been underway since May 02.
OIC Udawalawa Police, Inspector M. S. Dayawansa said the calf that deserted the herd had been released to the Udawalawa National Park in 2013 by the Wildlife Conservators.