Three people have been arrested following the deaths of multiple inmates at a prison in Bridgend.
Six prisoners died at HMP Parc between 27 February and 19 March.
Four of the deaths are believed to be drug related, while two are being treated as non-suspicious.
South Wales Police said a man, 40, from Birmingham, and a woman, 34, from Cardiff, were arrested on suspicion of conspiracy to supply controlled drugs and money laundering.
Both have been released under investigation.
A 34-year-old man, also from Cardiff, was arrested on suspicion of being concerned in the supply of controlled drugs.
He was released on conditional bail pending further enquiries.
'Found unresponsive'
On Wednesday, an inquest heard that one of the inmates who died, Cameron Andrews, was found unresponsive by prison staff during morning rounds on 19 March.
The inquest opening at Pontypridd heard that staff raised the alarm and performed CPR, but he died.
A post-mortem did not provide a cause for Mr Andrews' death, with further tests required.
But the assistant coroner for south Wales central, Rachel Knight, said she had reason to suspect that Mr Andrews' death may have been "unnatural".
The full inquest, which will be heard by a jury, was adjourned to a later date which is yet to be fixed.
HMP Parc is a category B prison holding convicted male adult and young offenders and convicted and remand sex offenders.
At the time of a 2019 inspection it held 1,612 prisoners, making it one of the largest prisons in the UK.