This undated photo provided by the Albemarle-Charlottesville Regional Jail shows James Alex Fields Jr. File picture: Albemarle-Charlottesville Regional Jail via AP

Charlottesville, North Carolina - Self-described neo-Nazi James Fields, who was convicted of killing Heather Heyer by ramming his car into a crowd protesting a white supremacist rally in Virginia in 2017, pleaded guilty on Wednesday in his federal hate crimes case.

Fields, 21, who previously pleaded not guilty to the federal charges, changed his plea during a hearing in U.S. District Court in Charlottesville, federal prosecutors said.

He is already facing a sentence of life in prison after being found guilty in state court of Heyer's murder and for injuring 19 in the college town in August 2017.

He faced 28 federal counts of hate crime acts causing bodily injury and involving an attempt to kill, and one count of racially motivated violent interference with a federally protected activity.

The specific charges that Fields pleaded guilty to were not immediately clear. The federal hate crime charges carried the possibility of the death penalty, but a plea deal could spare his life.

In December, a Virginia jury recommended that Fields spend the rest of his life in prison after finding him guilty of first-degree murder and nine other crimes for killing Heyer, 32, and injuring 19 people after the "Unite the Right" gathering in August 2017.

Fields, a resident of Maumee, Ohio, was photographed hours before the attack carrying a shield with the emblem of a far-right hate group. He has identified himself as a neo-Nazi.

Fields' attorneys never disputed that he accelerated his Dodge Charger into a group of counter-protesters at the rally, sending bodies flying. The lawyers suggested he felt intimidated and acted to protect himself.

The event proved a critical moment in the rise of the "alt-right," a loose alignment of fringe groups centered on white nationalism and emboldened by President Donald Trump's 2016 presidential victory.

Trump was criticized from the left and right for initially saying there were "fine people on both sides" of a dispute between neo-Nazis and their opponents. Subsequent alt-right gatherings failed to draw the crowds of the size that assembled in Charlottesville.