By Agence France-Presse
The spotlight is now on Rosmah Mansor after police last month raided two condominiums linked to Najib and his family as part of an investigation into his role in the 1MDB scandal -- seizing bags of cash, jewellery and hundreds of designer handbags.
Rosmah, 66, is widely reviled for her reported luxurious tastes and imperious manner. She last month issued a statement lashing out at media coverage of the police raids, calling them a "premature public trial".
Known for her love of luxury clothes and handbags, Rosmah arrived in a three-car convoy.
"Her questioning by graft busters will be intense and thorough," Abdul Razak Idris, former investigations and intelligence director at the Malaysia Anti-Corruption Commission (MACC), told AFP.
"She may also be asked to reveal her bank accounts and explain about the source of the cash and jewellery found by police in two condominiums recently."
Billions of dollars were allegedly stolen from the 1MDB fund -- founded by Najib -- in a sophisticated fraud that stretched from Singapore to Switzerland, with the money used to buy items ranging from Picasso artworks to high-end real estate.
Both Najib and the fund have consistently denied any wrongdoing.
The ex-premier has seen a swift fall from grace since he was defeated by a reformist coalition led by his former mentor, Mahathir Mohamed, in elections last month.
Voter anger at claims of corruption tied to Najib and a rise in living costs were among major factors in the shocking defeat of the ruling coalition, which had been in power for over six decades.
Najib himself was questioned by anti-graft officers twice last month. Both he and his wife have been banned from leaving the country.
The luxury-loving Rosmah is often compared with Imelda Marcos, who left behind more than a thousand pairs of shoes after her husband, Philippines President Ferdinand Marcos, was ousted in 1986.
In 2015, Rosmah told a public gathering that she paid 1,200 ringgit ($300) to colour her hair, angering Malaysians as the minimum wage was then just 900 ringgit a month.