The first five days of former prime minister Najib Abdul Razak's 1MDB graft trial has seen his former special officer Amhari Efendi Nazaruddin emerge as an important witness for the prosecution.

Amhari, 43, who worked for Najib for around 10 years, had provided details on the inner-workings of officers in the Prime Minister's Office (PMO) and their heavy dealings with 1MDB-linked businessperson Low Taek Jho, or better known as Jho Low.