Malaysia's top court ordered former prime minister Najib Razak to begin a 12-year prison sentence on Tuesday after upholding a guilty conviction on charges related to a multi-billion dollar graft scandal at state fund 1Malaysia Development Berhad (1MDB).

The Federal Court ruling caps the stunning downfall of Najib, who until four years ago governed Malaysia with an iron grip and suppressed local investigations of the 1MDB scandal that has implicated financial institutions and high-ranking officials worldwide.

Prosecutors have said some $4.5 billion was stolen from 1MDB — co-founded by Najib during his first year as prime minister in 2009. Investigators say they had traced more than $1 billion of 1MDB money to accounts linked to Najib.