Ray Abou-Arab, 61, appeared in Toledo Municipal Court, where Judge Denise Ann Dartt set bond at $2 million for each of two aggravated murder charges and $500,000 each for two aggravated arson charges, the Toledo Blade reported.
Police said Abou-Arab set fire to an apartment building he owned last week. His motive for doing so remains unclear.
Two firefighters responding to the blaze, Pvts. Stephen Machcinski and James Dickman, became trapped in the burning structure and were killed.
About 50 of their fellow firefighters staged a march Monday in their honor, gathering at their union headquarters and walking several blocks to the courthouse. They packed the gallery and held photos of the two men.
"The idea behind this is just making sure that we have a presence there," Toledo Firefighters Local 92 President Jeffrey Romstadt said. "Usually family show up for arraignments to make sure that things happen correctly, and we'll be there to give our support to fallen brothers."