Could you post a screenshot of your Senate Floor panel, Bach01? I´d like to see what the respective support from Senate and Plebs is. I´m pretty sure you can´t attack another Roman faction if the support from the plebs is too low.

And yes, it´s a failed assasination attempt that gets you outlawed, if it´s sucessful, or fails with the assasin escaping alive no one knows you´re behind it.