Two men are being questioned about the deaths of two teenagers from carbon monoxide poisoning.
Aaron Davidson and Neil McFerran, both 18, from Newtownabbey died at a holiday apartment in Castlerock last August.
Detectives are questioning the men - aged 40 and 49 - about the friends' deaths.
It is understood Coleraine gas fitter George Brown is one of the men being interviewed by police.
The teenagers had been staying at the apartment near Coleraine with a third friend, Matthew Gaw, who survived. The three friends were found by relatives.
Following the deaths the Health and Safety Authority launched an investigation into a carbon monoxide leak from a faulty appliance in the flat.
It received more than 600 calls after urging anyone who had work carried out by Mr Brown, trading as George Brown Calor Gas in Coleraine, to switch off gas appliances immediately.
The Calor shop run by Mr Brown is an entirely separate legal entity to Calor Gas (NI) Limited.
The HSE's investigation is ongoing.