Mr Aiken goes through Mr Cooper's version of the state of affairs at DETI in 2013.

Mr Cooper was off sick for six months that year.

The inquiry lawyer says an overarching point in Mr Cooper's witness statement is that DETI's finance division was "under significant pressure on a constant basis with the processes that had to be carried through".

Image source, Getty Images

There was not a lot of scope to look at things beyond "what you had to get done" and that there was a high load of case work at the time.

The first time Mr Cooper said he became aware of the RHI scheme was May 2015.

Trevor Cooper (below) has appeared twice before - in February and March this year.

For most of the time the inquiry is interested in, Mr Cooper was a finance director at DETI.

Image source, RHI Inquiry

Inquiry junior counsel Joseph Aiken takes a run through the areas we'll be looking for today.

Mr Cooper confirms that he has given further written evidence to the inquiry since his last appearance.

An independent inquiry into the RHI scandal was established in January last year by the then finance minister Máirtín Ó Muilleoir.

He ordered it in the wake of the huge public concern and what was then a major political crisis surrounding the scheme.

The RHI Inquiry began in November last year and Sir Patrick Coghlin (below), a retired Court of Appeal judge, is its chair and has been given full control over how it will operate.

Image source, Pacemaker

It is looking at:

• the design and introduction of the RHI scheme
• the scheme's initial operation, administration, promotion and supervision
• the introduction of revised subsidies and a usage cap for new scheme claimants in autumn 2015
• the scheme's closure in February 2016

For more information on the RHI Inquiry, you can read our handy Q&A.

When the scale of the overspend emerged, public and political concern rocketed.

As the minister in charge of the Stormont department that set up the RHI scheme, the DUP leaderArlene Foster faced calls to resign from her roleas Northern Ireland's first minister in December 2016.

She resisted, and Sinn Féin's Martin McGuinness then quit as deputy first minister in protest at the DUP's handling of what had by then become a full-blown political crisis.

That move brought about the collapse of the Northern Ireland Executive. Now, well beyond a year-and-a-half on from that, Northern Ireland remains without a devolved administration.

You can find much more detail on the RHI scheme in our need-to-know guide.

The budget of the RHI scheme ran out of control because of critical flaws in the way the initiative was set up.

Claimants could effectively earn more money the more fuel they burned because the subsidies on offer for renewable fuels were far greater than the cost of the fuels themselves.

At one point the estimate for the overspend was set at £700m if permanent cost controls weren't introduced - temporary cuts have since pulled the budget back on track for now.

Whatever the scale of the bill, it will have to be picked up by the Northern Ireland taxpayer.

The Renewable Heat Incentive scheme - or RHI for short - came to the fore of the Northern Ireland public's knowledge in late 2016.

The fallout from the scandal attached to it is still being felt in the region's politics today.

The scheme was set up by the Northern Ireland Executive in 2012 as a way of encouraging businesses to switch from using fossil fuels to renewable sources for generating their heat.

Those who signed up were offered financial incentives to buy new heating systems and the fuel to run them.

Image source, PA

It's Wednesday, so it must be Day 105 of the RHI Inquiry here on the hill at Stormont.

Today's witness is civil servant Trevor Cooper.

Mr Cooper was head of finance at the Department for Trade and Investment (DETI).

The session starts in a few minutes.

We'l have live video all through the day, and reporting on all the important bits.

Do stay with us.