The head of the Northern Ireland Civil Service has said he wished he had been more inquisitive when the Renewable Heat Incentive (RHI) scheme was being explored.
David Sterling was permanent secretary at the Department of Enterprise, Trade and Investment at the time.
He told a public inquiry he did not have the "foresight" to direct more resources towards project management as the novel and flagship RHI policy was worked up.
Mr Sterling gave evidence to the RHI public inquiry at Stormont and chairman Patrick Coghlin queried why such a volatile and unpredictable scheme did not attract more of his personal interest.
Mr Sterling said once issues were raised by a concerned citizen and regulator Ofgem the energy team involved should have paused their work and, if worried, contacted him.
He added: "I should perhaps have been more inquisitive. I should perhaps have stood back and said maybe I do need to look at this and become more closely involved.
"There were a range of controls and factors which were in place at the time which I would have taken comfort that the scheme was going to be managed well."
The public inquiry is investigating the non-domestic scheme after it ended up paying out more in subsidies than it cost to buy fuel and costs to the public purse rose massively.
Mr Coghlin said it was a complex scheme, it was the first of its kind, and that fact was not observed by the upper regions of the Civil Service at the time.
He said only three people, two part-time, were working directly on it within the department and the person who did all the "donkey work" had no qualifications in energy, he added.