Why didn't the Capitol bomb District 13

As seen in Mockingjay part 1, the Capitol, and President Snow, knew where 13's underground base was located. Did they just get that information ? Or was it known for a long time ? If so, why didn't they just bomb it sooner, or even a little time after the Dark Days. That way, they could've ensured they wouldn't start a rebellion again, like they already did.