One of Arlene Foster's ministerial colleagues has claimed political rivals calling for her resignation as Stormont First Minister are more interested in a scalp than the truth.
Stormont Economy minister and fellow Democratic Unionist Simon Hamilton defended his party leader after a renewed wave of calls for her to step aside over her handling of a botched green energy scheme.
He accused opposition MLAs attacking the DUP leader over the Renewable Heat Incentive (RHI) scandal of offering nothing more than "party political attacks and resignation calls".
"On the one hand they call for a process to establish the facts but they have already decided what the outcome should be," he said.
Mr Hamilton was reacting to the publication of a letter Mrs Foster sent to bankers about the RHI when she was economy minister in January 2013.
In it she said payments made under the scheme would be "guaranteed" - an assertion that prompted rivals to rubbish her current stance that half of the estimated £490 million overspend could be clawed back.
In the two-page letter to Northern Ireland's leading banks, Mrs Foster said the state-funded eco-subsidies offered applicants a "good return on investment".
Errors in the RHI have left Stormont facing a huge overspend bill over the next 20 years.
It was supposed to offer a proportion of the cost businesses had to pay to run eco-friendly boilers, but the tariffs were set too high, and without a cap, so it ended up paying significantly more than the price of fuel.
This enabled applicants to "burn to earn" - getting free heat and making a profit as they did it.
Claims of widespread abuse include a farmer allegedly set to pocket around £1 million in the next two decades for heating an empty shed.
Mr Hamilton, who issued a statement through the DUP, not his department, said Mrs Foster wrote the letter before the fatal weaknesses in the scheme came to light.
"These letters, issued in 2013, once again highlight the fact that there was a significant underspend in the early years of the RHI scheme and far from highlighting an awareness of the issues which have subsequently come to light, further reinforce the fact that the department was operating, at that time, under a serious misapprehension about the scheme," he said.
He added: "Had the scheme operated as described in the letter then the present problems would not exist.
"The DUP supports an investigation which can be entirely free from political interference and which can report speedily in order to assist public confidence."
Jim Allister, leader of the Traditional Unionist Voice party, said: "So the DUP's latest excuse for the biggest taxpayer rip-off in our history is that Arlene Foster acted under a 'misapprehension' when she approved the RHI scheme.
"So incompetence in government is now the DUP's refuge - a commentary in itself."
Mrs Foster, who was in charge of the scheme's development during her time as economy minister, has faced down calls to quit from all the other main Stormont parties, including the DUP's partner in the ruling executive, Sinn Fein.
She has remained defiant amid the "ash for cash" furore and insisted the projected overspend can be halved.
That prediction was challenged after the contents of the bank letter were revealed on Thursday night.
She wrote: "Tariffs are 'grandfathered', providing certainty for investors by setting a guaranteed support level for projects for their lifetime in a scheme, regardless of future reviews."
Mrs Foster added: "The government support, on offer through the incentive schemes, is reliable, long term and offers a good return on investment."
The letter was written to encourage banks to lend to would-be RHI applicants who needed initial capital to purchase the costly green boilers.
Ulster Unionist leader Mike Nesbitt claimed the First Minister's leadership was characterised by "incompetence, ineptitude and haplessness".
"Mrs Foster has not only failed to do the honourable thing, by accepting the consequences of ministerial responsibility and resigning, she has spun a web in which she now finds herself trapped, ensuring a legacy of debt to be paid by children yet to be born, and leaving her reputation as a competent minister in tatters," he said.
SDLP leader Colum Eastwood said: "Arlene Foster's instinctive resistance to calls for her to stand aside pending a public inquiry is understandable but it is fundamentally misguided.
"This is about more than the career of one politician. The longer the First Minister stays, the more lasting damage she does to the institutions and to faith in government.
"If Arlene Foster has done nothing wrong, as she claims, then she has nothing to fear from a public inquiry with full powers to compel witnesses and evidence."
It was originally envisaged that the Treasury would foot the bill for the RHI, but the costs spiralled well beyond London's financial commitment. The total RHI spend in Northern Ireland is estimated at £1,150 million over the next 20 years.
The Treasury is set to cover £660 million of that, with Stormont landed with the remaining £490 million.
A spokeswoman for the Department for Economy said Mrs Foster's letter was "reasonable and appropriate" given the context facing the minister in January 2013.
She said the flaws in the scheme were not well documented at the time the letter was written.