New Zealand's market regulator has written to Ross Asset Management investors trying to get information to help its probe of the collapsed Wellington firm.
"Substantial enquiries have already been conducted by the investigation team, and the further information sought here is very important to our investigation," the FMA's Jason Lunjevich said in the letter.
The authority is looking for information specifically from those who still had money with RAM last September, around a month before the firm and the home of its founder, David Ross, were raided by the FMA.
Ross was still winning over clients at this time and some investors were even considering giving him more money.
Just weeks before the FMA raided RAM in November last year, investors who met him were convinced their money was "as safe as houses".
After raiding RAM, the FMA obtained freezing orders of the Ross group's assets and those of associated entities.
Receivers from PwC were then appointed by the High Court but could find only approximately $11.1 million of the $450 million Ross' clients thought they had invested.
PwC's John Fisk said last year the receivers had found "characteristics of a Ponzi scheme" at RAM.
The receivership was wrapped up last month and RAM is currently in liquidation.