The PSNI is examining allegations of fraud in how some MLAs claimed their expenses.
lan McQuillan from the Independent Financial Review Panel set up to examine the Stormont expenses system said it had been a "free-for-all".
Alliance leader David Ford spoke of "potential fraud in the region of tens of thousands of pounds".
In an explosive two-part BBC Spotlight investigation it was alleged:
- 36 Sinn Fein MLAs paid over £700,000 to a research agency with no visible outcomes.
- Agriculture Minister Michelle O'Neill claimed £18,000 rent a year for an office in Gulladuff near Maghera, which one trustee has insisted is owned by Sinn Fein.
- DUP MLA Willie Hay's office claimed more than £4,000 for heating oil expenses in one year.
- UUP and SDLP MLAs were claiming thousands from their office cost allowances (OCAs) into their parties centrally to pay for staff.
Yesterday the PSNI confirmed that detectives from Serious Crime Branch are currently "scoping allegations of potential criminality made in recent media reports".
Justice Minister David Ford said there was a "significant suspicion that a number of MLAs abused the expenses system".
"These allegations will only further put people off politics following the offensive comments by Gerry Adams and Gregory Campbell," he said.
"The criticism of the programme makers by certain politicians has also angered the public.
"These allegations are in danger of causing serious damage to the political process."
He added that it is "vital that there is openness and transparency in politics and that the public can be confident that expenses are being used appropriately."
Yesterday in the wake of the Spotlight programmes a public online petition was established urging Prime Minister David Cameron to ensure an independent investigation of the Assembly's expenses system.
Former Alliance Party MLA Seamus Close told Spotlight he had witnessed a culture at Stormont where if money was available, it should be claimed.
"There was this culture that if there was an OCA of £30,000, then Members should spend that £30,000," he said.
"I know for a fact that there were those that thought I was insane because I didn't spend it all."
Mr McQuillan, one of the three members of the Independent Financial Review Panel set up to examine MLA expenses, echoed this, saying the system had previously been a "free-for-all".
He said the panel was in the midst of a major review of the system.
"We were formed in 2011 and because we came in in the middle of a mandate, MLAs had already rented their premises and hired their staff," he told the Belfast Telegraph.
"There was only so much we could do, but we have been working away preparing for the next mandate."
Mr McQuillan said the average MLA pays around £6,000 for their office, but some paid over £20,000.
"We want to change all that and also address the issue of transparency - who they actually rent from," he said.
"We were not surprised by Spotlight but there were some new issues they raised that we will be pursuing, such as some of the issues around Research Services Ireland Ltd and the property interests of individuals and the postage stamps.
"We want to look at that and get to a system which is honest and transparent.
"Now is the time for a major tightening of the restrictions."
He added that most MLAs had been prudent with public money.
Chairman of the Assembly Standards and Privileges Committee Alastair Ross said he will be ask the Assembly Commission to ensure that the system is properly reformed. "Expenditure should not only be scrutinised by an independent body, but the rules governing that spending must also be set independently," the DUP man said.
"Where there have been allegations of a potentially criminal nature it is absolutely right that these are investigated by the police.
"The DUP will fully support such changes and I believe that other parties will do likewise."
Sinn Fein MLA Raymond McCartney has insisted his party has nothing to worry about with an investigation into the system.
"My party has nothing to fear and my party has nothing to hide," he said. "Everything we claim is on behalf of the people who have elected us to do a job in the Assembly."