Indonesia’s Attorney-General’s Office arrested Pertamina International Shipping chief executive Yoki Firnandi late on Monday on suspicion of playing a part in what prosecutors allege to be one of the largest corruption scandals to hit the Asian nation in many years.

Firnandi was one of three key executives who headed subsidiaries of state-owned oil giant Pertamina who were detained amid allegations of violating government regulations requiring Pertamina to source crude oil from domestic suppliers.