A 20-year-old man was charged on Sunday with first-degree assault in last week's shooting of two policemen during a protest rally in Ferguson, Missouri - a crime that shocked a city that has been devastated by months of racial strife.

The suspect, Jeffrey L. Williams, admitted to firing the shots that wounded the officers early on Thursday, according to St. Louis County Prosecuting Attorney Robert McCulloch.

The gunfire rang out just after midnight at the end of a rally calling for sweeping reforms in Ferguson, where an unarmed black 18-year-old was shot to death by a white officer in summer.