Police spokesman Kombes Winardy told Antara that the arrests follow a month-long investigation and that a sixth suspect is being pursued.
He added that the elephant was initially discovered in a palm oil plantation in Jambo Reuhat village in the Banda Alam District and that an autopsy had confirmed poisoning to be its cause of death.
Indonesian conservation law prohibits the killing and trading of protected animals like Sumatran elephants; if found guilty, the men could face fines and up to 10 years imprisonment.
Only around 2,400—2,800 of the elephants survive in Sumatra and Borneo, according to the World Wildlife Fund (WWF), making them critically endangered.
But despite this, poaching remains common. In 2019, two Sumatran elephants were found dead in the space of a week, one of them on a plantation in Aceh.
The animals frequently enter the plantations to feed on palm oil fruits where they are targeted by poachers for their ivory.