The Natore units of the ruling Awami League's youth front organised a news conference after the bodies of the trio were found in Ghorhaghat Upazila on Monday morning.
The Juba League leaders said they suspected it was 'planned murders', but did not say whom they suspect.
Natore Municipality Juba League Convenor Sayeem Hossain said, "We can't say who have killed our leader and activists after abduction and why."
The three are Natore Municipality Juba League convening committee member Redwan Sabbir, 30, and activists Sohel Rana, 24, and 'Abdullah', 25.
He also said four mobile phones were found on the bodies and three of them were password-protected.
Natore district Juba League acting General Secretary Ruhul Amin said at the press conference that Sabbir, Sohel and Abdullah were whisked away by 15 to 16 miscreants on two microbuses from a tea stall at Tokia Bazar around 11pm on Saturday.
Sabbir's mother filed a missing person complaint at Sadar Police Station on Sunday.
Sayeem said it was a 'planned murders' and demanded immediate identification and arrest of the perpetrators.
He said the deceased had several cases against them. Sabbir was released on bail on Thursday, he added, but did not say what the charges they were facing.
The families of the victims also did not speak over the cases against the trio.
The bodies were being taken back to Natore after post-mortem examination in Dinajpur Medical College Hospital, they said.