The chair of a public inquiry has said the DUP was run in an "unpleasant" way.
Retired judge Sir Patrick Coghlin heard evidence from former party special adviser Tim Cairns in relation to the botched renewable heat incentive (RHI) green energy scheme in Northern Ireland.
Mr Cairns told him he had not tried to smear his former boss, ex-Stormont enterprise minister Jonathan Bell, over the affair.
Sir Patrick said the "clear inference" was that he was prepared to modify his comments about Mr Bell to protect former DUP leader Peter Robinson.
Documents before the inquiry, including a text message from Mr Cairns to another party special adviser, showed he was prepared to, in his words, fit his story into the party's "narrative".
Sir Patrick added: "That seems a rather unpleasant way to run a party."
Mr Cairns denied any plan to fit Mr Bell up.
The former special adviser said he was being contacted by journalists constantly in December 2016, despite being outside Northern Ireland, and had sought help after Mr Bell disclosed his version of events surrounding the out-of-control heating scheme.
Mr Cairns said politics was a "grubby world" and the inquiry chairman responded that was an understatement.
Much of the former party official's evidence contradicted Mr Bell's version of events, discussed during the ex-Assembly member's colourful evidence sessions before the inquiry last week.
The green energy scheme paid over-generous subsidies to wood fuel burner owners.
Concerns centre on how long it took to close after civil servants became aware of the flaws and the DUP's alleged role, if any, in manipulating that closure date.
The devolved powersharing institutions collapsed early last year after Sinn Fein walked out over the DUP's handling of the RHI and repeated rounds of negotiations have failed to resurrect them.