A pit manager who survived a flooding incident in which four miners died has been arrested on suspicion of gross negligence manslaughter.
Malcolm Fyfield, 55, was held by officers from South Wales Police investigating the accident at the Gleision Colliery near Swansea last month.
David Powell, 50, Philip Hill, 44, Garry Jenkins, 39, and Charles Breslin, 62, died after floodwater engulfed a tunnel where they were working on the morning of September 15.
Fyfield was able to escape from the mine and was taken to hospital. His condition was reported as critical at the time.
South Wales Police did not name the suspect, who was arrested in the Swansea Valley on Tuesday morning and is being held at Port Talbot police station.
The victims' families and community leaders were informed of the arrest.
Detective Chief Inspector Dorian Lloyd, the senior investigating officer in the case, said: "The arrest follows consultation between South Wales Police, the Health and Safety Executive and the Crown Prosecution Service to review the evidence gathered to date.
"We continue to work closely with the bereaved families throughout this process and I would like to express my sincere gratitude to the communities affected by this incident for their continued support and patience.
"We will do everything possible to fully understand how these four men lost their lives."