US prosecutors are looking at the relationships and account flows of former Goldman Sachs banker Tim Leissner, who was instrumental in arranging for three bonds for 1MDB which were later allegedly siphoned off.

According to Bloomberg, the US Federal Bureau of Investigation (FBI) and Justice Department have been interviewing bankers familiar with 1MDB about Leissner's relationships with politically-connected Malaysians.

The report, citing people familiar with the investigations, said the interviews focused on, among others, Leissner's relationship with Penang-born billionarie Jho Low, who was a key figure in structuring 1MDB's fund flows across the globe.

Leissner helped arrange two bonds totalling US$3.5 billion in 2012, and another US$3 billion bond in 2013 for 1MDB.

According to the DOJ, at least US$1.367 billion from the first two bonds and another US$1.26 billion from the third bond were allegedly siphoned off.

The report said investigators have also been examining Leissner's interactions with his former Goldman Sachs colleague Roger Ng.

Ng, a Malaysian, was head of Goldman Sachs' Southeast Asian sales and trading business, it said.

The report said Ng and Leissner's lawyer March Harris had declined to comment.

Ng left Goldman Sachs in 2014 while Leissner quit last year.

The DOJ believed at least US$3.5 billion was misappropriated from 1MDB and is in the process of seizing around US$1 billion in assets allegedly acquired using diverted 1MDB funds.

Malaysiakini is unable to independently verify the report.