Federal agents arrested two more Capitol Hill rioters whose images had gone viral, of one carrying off the House Speaker’s lectern and another who wore horns and a fur pelt, while a top Democratic lawmaker called on mobile carriers to preserve social media content related to the carnage.

Dozens of people have been charged following the storming of the Capitol on Wednesday, with the FBI asking the public to help identify participants, given the proliferation of images of the riots on the Internet. Five people have died, including a police officer.

Jacob Anthony Chansley, who featured prominently on social media...