The FBI planted bugs in Oakland courthouse without a warrant

Reading up a bit more, the question of whether FBI behaviour here was illegal seems like the kind of thing I’d want to consult a lawyer about. It sounds shady, but when the defense asserts:

"Speaking in a public place does not mean that the individual has no reasonable expectation of privacy,"

Is that actually true in the US? 'cause I’m not a lawyer, but I thought it wasn’t.