'Plastic container exploded under Cardiff prison stairwell'
Four men have been arrested after an explosive device was made at Cardiff prison.
South Wales Police said a bottle containing an unknown liquid "erupted and slid across the floor" on 15 June.
Three of the men are under investigation while one will face no further action. The incident only came to light when a prison worker contacted South West Wales AM Bethan Jenkins.
Mark Fairhurst of the Prisoner Officers' Association said a plastic container placed under a stairwell exploded and an internal investigation was under way.