Yup all the bugs were illegal back then. It was just pretty much for information so they can find out where they go and what they do. Stop murders before they happen.
If you think about it all the people he was following died in their beds not in jail.
Exception being Giancana cause he was killed.
Roemer was pretty much a very big thorn in their sides. Always there when they didn't want him to be. Not many successful prosecutions just arrests. Times and laws were very different back then.