Police were investigating Stephen Brimstone's application to the botched RHI scheme while he was a special adviser to the First Minister.
The Irish News can reveal that PSNI received concerns about the former DUP aide back in October last year, a month before Mr Brimstone resigned from his £91,000 -a-year position, and made enquiries with regulator Ofgem into the matter.
Police were alerted to anonymous allegations of fraud concerning the non-domestic scheme in a letter sent by TUV leader Jim Allister on October 10, 2016.
The response dated November 11 said police had "no cause for concern" regarding Mr Brimstone's RHI application, but reference is made to an investigation of alleged abuse of the 'domestic', rather than the non-domestic scheme.
"I can advise that police made enquiries with Ofgem in respect of this matter. They verified that Mr Brimstone's application to the RHI scheme was fully compliant and they have no cause for concern," she wrote.
"As a result of the enquiries made, I can confirm that no crime has been committed," a Detective Sergeant added.
Mr Allister also contacted the Northern Ireland Audit Office and Ofgem in October, relaying the same anonymous allegations, with the NIAO stating they would "take it into account in our enquiries".
Ofgem said they were "unable to discuss the details of specific individuals" due to data protection laws.
The response did state however that "an installation providing heat to both a domestic and a non-domestic use may well be eligible" for the non-domestic scheme.
Former First Minister Arlene Foster revealed last month that Stephen Brimstone was an RHI claimant, but neither her nor the party would disclose the details. The DUP denied his resignation at the end of November was due to the green energy scheme, but rather to "pursue opportunities in the private sector".
At Mr Brimstone's home in the greater Ballymena area a large shed with solar panels sits beside a two-storey house. It is not clear whether the shed contains a wood pellet boiler or the nature of the business within. Just beside the building is a small outdoor chicken coop.
Under parliamentary privilege in Stormont Jim Allister claimed that Mr Brimstone is using a non-domestic RHI boiler to heat his home. He further alleged on Monday that the former special adviser previously had a biomass boiler, but then took it out and installed a different boiler under the RHI's more lucrative non-domestic tariff.
When asked if police were currently investigating Mr Brimstone in relation to the RHI scheme, Detective Chief Superintendent Tim Mairs said: "The Police Service are in regular contact with both OfGem and the Department for the Economy in respect of their reviews of the Renewable Heating Incentive (RHI) Scheme and we have agreed that any matters which indicate the possibility of criminal conduct should be referred to the PSNI at the earliest possible opportunity. To date, both bodies have confirmed to me that they have not identified any cases meeting this criteria."
A spokesman for Ofgem said: "Ofgem has a zero tolerance approach to fraud. We have a dedicated counter fraud team who work to prevent, deter and detect fraud across the environmental or social programmes we administer on behalf of the Government. We do not comment on individual investigations we conduct."
Mr Brimstone has yet to make any comment in relation to the RHI allegations.
