It happened just before 2 am Sunday morning, which is about the same time as a similar explosion at a Federal Express facility a week ago. That has agents looking into whether they're the work of an organized group, like a terrorist organization.
"I don't know they would choose this target to do this I am just thankful it occurred at the time it did so there weren't any injuries just property damage," said FBI Special Agent Keith Slotter.
There's a smashed window up high too. Agents even found debris and damage eight stories up on a building that faces the courthouse.
Bomb experts will analyze the evidence from San Diego in a lab near Washington D.C.