A Brazilian federal prosecutor announced qualified manslaughter charges Thursday against 21 people, including senior executives, allegedly responsible for the deadly collapse of the Samarco iron ore mine dam last year.

The prosecutor, Jose Leite Sampaio, made the announcement in a televised press conference in Belo Horizonte, near the site of the disaster on November 5, 2015, when the failed dam unleashed a torrent of muddy water killing 19 people. It was branded Brazil's worst ever environmental disaster.