The court is focusing on two payments made by the French arms dealers Thales International and DCNS, allegedly to secure the contract to provide two Scorpene submarines to the Malaysian navy.
At the time of the payments Najib was defense minister. The court will pay particular attention to the role of Najib's policy adviser, Abdul Razak Baginda, in the payments.
One payment, for 114 million euros, was made to the Malaysian company, Perimekar, for "logistical support." Baginda and his wife were sole owners of the company at the time of the deal.
Another payment of 35 million euros was made to a company called Terasasi, of which Baginda and his father were registered directors.
Adding to the drama, is the the investigations connection with the murder of Mongolian model and translator Altantuya Shaariibuu, whose body was found outside Kuala Lumpur, on October 2006.
An ex-lover of Razal Baginda, Aalantunya had worked as a translator on the Scorpene deal in 2004. She was last seen outside Baginda's house, and a handwritten letter found after her death suggested she would demand $500,000 from Baginda to keep silent on the bribery scandal.
Baginda was charged with Altantunya's murder, along with Najib's bodyguards. Baginda now lives in exile in Britain, while the bodyguards face the death penalty. They are currently appealing the ruling.