In Chapter 15 of "To Kill A Mockingbird," who is "covering" Atticus during the mob incident at the jailhouse?

As Atticus protects jailed Tom Robinson from an mob of vigilantes, Mr. Underwood, the owner of the Maycomb newspaper, is positioned from a second-story window with a double-barreled shotgun pointed at the angry men. When the lynch mob leaves, Atticus and the children discover Mr. Underwood as he says, “Had you covered all the time, Atticus.”

Ironically, Mr. Underwood does not make himself known to the mob. Some critics say it is because he was afraid of retaliation or of being shunned from society for protecting Atticus, a man who was defending a black "rapist." Mr. Underwood is also know to "despise" black people.