The Serious Fraud Office (SFO) has closed its investigation into a group of companies formerly controlled by an ex Wall Street banking corporation director, saying it did not have sufficient evidence to lay criminal charges.

The SFO launched an investigation into WSD Global Markets Limited and related companies last October after claims the group failed to correctly account to investors for funds received.

WSD was previously controlled by former Wall Street Banking Corporation Director, Riaz Patel.

Serious Fraud Office chief executive Adam Feeley said the complaints mainly related to debts arising out of deposits with WSBC, a bank in the Cook Islands which was placed in judicial management following termination of its Cook Islands banking licence.

While there was some misunderstanding as to the identity of the company within the WSD Group that owed the obligations and the terms upon which they were owed, the investigation concluded these were commercial issues, he said.

"The SFO did not identify material evidence to suggest that the misunderstanding arose from fraudulent activity," Feeley said.

"The fact that persons have not had their debts repaid is not in itself fraud. This, coupled with some considerable difficulties in securing sufficient cooperation with many of the overseas complainants, has prevented us from taking this matter any further."

Feeley said the decision not to take the investigation further should not be interpreted as an approval or endorsement of the WSB businesses by the Serious Fraud Office.

"The only message taken from the SFO's action should be that in relation to the specific complaints looked at, the evidence available was not sufficient to support the laying of criminal charges."