The manager of a colliery where four miners died has been charged with fours counts of manslaughter, police said.
Charles Breslin, Philip Hill, Garry Jenkins and David Powell died at the Gleision mine near Pontardawe, south Wales, in 2011.
Today police announced that pit manager Malcolm Fyfield, 57, has been charged with four counts of gross negligence manslaughter.
The company which owns the colliery, MNS Mining Ltd, has also been summonsed to answer four counts of corporate manslaughter.
Detective Chief Inspector Dorian Lloyd, of the South Wales Police Specialist Crime Investigations Team, said an extensive investigation had been carried out by police and the Health & Safety Executive.
He said: "The aim of this investigation was to establish a full understanding of the events that led to such devastating loss of life.
"Upon completion of the investigation and following consultation with the Crown Prosecution Service, the mine manager, Malcolm Fyfield has today been charged with four counts of gross negligence manslaughter.
"In addition, a prosecution for four offences of corporate manslaughter against the owners of the mine, MNS Mining Ltd, is proceeding."
A major rescue operation was launched at the small hillside mine following its sudden collapse.
Mr Fyfield was seriously injured in the incident, but escaped through an old mine shaft.
Two other miners, including Mr Powell's son, escaped and helped raise the alarm.
Coming just weeks after the rescue of trapped Chilean miners, at the time there had been genuine hope that the four men would be found alive.
Their distraught families - along with an entire country - waited with bated breath for good news.
But as the hours went on, the trapped miners' bodies were discovered one by one.
Since then, their families have described the wait for answers into the deaths as agonising.
Neath Labour MP Peter Hain, who launched a charity fund for the dead men's relatives which topped around £1 million, welcomed the development in South Wales Police's investigation.
He said: "After such a devastating tragedy, the families and our communities have naturally been anxious to discover why and how the four local miners were killed.
"This prosecution will enable the truth to be revealed for the first time."