The United Mine Workers of America has urged federal regulators to conduct a free and public hearing on the deadly explosion at West Virginia’s Upper Big Branch mine.

An open investigation will allow the Mine Safety and Health Administration (MSHA) to subpoena witnesses, which will be critical to learning the truth, United Mine Workers of America president Cecil Roberts said.

Roberts added that a public hearing will allow the MSHA to compel witness to testify and also provide information quickly to the families of the 29 men killed in the 5 April explosion.

Meanwhile, the widows of two men killed in a 2006 fire at a Massey coal mine run by its Aracoma unit have sued the MSHA, alleging improper inspections linked to the deaths.