A suspect arrested over the incident made the claim in his testimony to court, said Md Shafikul Islam, Deputy Inspector General (DIG) for Chittagong Range.
Accused Nurul Absar said the Rohingya Solidarity Organisation (RSO) was involved in the attack from May 13.
They shot dead barrack commander Md Ali and looted 11 firearms and 690 rounds of ammunition.
Police arrested three suspects but Absar is the only one shown arrested in the case. The 22-year-old hails from Hnilar Rangikhali.
The news of his arrest was made public on Monday but police did not say where they caught him.
“Suspect Nurul Absar described the entire attack before court. He said Myanmar nationals, a Pakistani and several Bangladeshis took part in it,” DIG Shafikul told reporters.
“The plan put to use RSO members from Chittagong, Rohingya people who arrived by boat, on the night of the attack… some more from the camp and some Bangladeshis.”
The main plan was to rob weapons and most of these attackers had fled to Myanmar with those weapons, said the DIG.
Absar had fled with them but was caught when he tried to re-enter Bangladesh.
A joint force of security agencies was working to reclaim the firearms and arrest those involved, he said.