John Pierce, the right-wing lawyer representing 17 defendants accused of storming the Capitol, has failed to appear at several court appearances over the past week, sparking the Justice Department to issue a rare warning that Pierce’s sudden disappearance could jeopardize his clients’ cases.

The filling on Monday pointed to reports, as well as an explanation from Pierce’s colleague Ryan Marshall, indicating that Pierce, an outspoken anti-vaxxer, is seriously ill from COVID-19 and possibly unresponsive on a ventilator.