Charlottesville's police chief, who oversaw the department's widely criticized response to a violent white nationalist rally this summer, abruptly retired Monday, the city said.

In a brief statement, the city did not give a reason for Chief Al Thomas' departure.

Earlier this month, a former federal prosecutor released a report that was sharply critical of Thomas' 'slow-footed response' as the violence began to escalate on August 12, the day of the 'Unite the Right' rally that drew hundreds of white nationalists from across the country.

Scroll down for video

Charlottesville Police Chief Al S. Thomas Jr. exits the memorial service for Heather Heyer, at the Paramount Theater in Charlottesville, Virginia on August 16

Thomas Jr. stands outside the Paramount Theater during a memorial service for Heather Heyer

Heather Heyer, 32 was killed that day when a car plowed into a crowd of people after the white nationalist rally.

James Fields, 20, from Ohio, is accused of driving the vehicle that killed Heyer and injured dozens of others.

He has been charged with first degree murder, upgraded on Thursday from his initial charge of second-degree murder by District Judge Robert Downer, the Richmond-Times Dispatch reported.

The report also said Thomas deleted relevant text messages and made officers fearful of retaliation for speaking with investigators.

James Fields (R), 20, from Ohio, is accused of driving the vehicle that killed Heyer (L)

A former federal prosecutor released a report that was sharply critical of Thomas' 'slow-footed response' as the violence began to escalate on August 12, the day of the 'Unite the Right' rally that drew hundreds of white nationalists from across the country

Charlottesville's police chief, who oversaw the department's widely criticized response to a violent white nationalist rally this summer, abruptly retired Monday

Kevin Martingayle, an attorney for Thomas, has said the chief disputes that he deleted text messages. Martingayle didn't immediately return a message from The Associated Press seeking comment.

City Manager Maurice Jones called Thomas 'a man of integrity who has provided critical leadership for our department since his arrival.'

'We wish him all the best in his future endeavors,' he said.

The report also said Thomas deleted relevant text messages and made officers fearful of retaliation for speaking with investigators

The 'Unite the Right' rally on August 12 drew hundreds of white nationalists from across the country and left one woman dead

The city's statement said Deputy Police Chief Gary Pleasants will guide the department until an interim chief is formally appointed within the next week.

'Nothing in my career has brought me more pride than serving as the police chief for the city of Charlottesville,' Thomas said in the release.

'I will be forever grateful for having had the opportunity to protect and serve a community I love so dearly. It truly has been an unparalleled privilege to work alongside such a dedicated and professional team of public servants. I wish them and the citizens of Charlottesville the very best.'

A veteran of the Air Force, Thomas was appointed police chief in April 2016 and began his service the following month, according to the statement.