That's what I was thinking. A few months ago I had jury duty (In Honolulu). There were metal detectors at all entrances to the courthouse and even the LEOs entering the building had to surrender thier weapons and have them put in a locker outside. The bailif, if I recall correctly, was not armed. I thought that that was pretty much standard procedure all over the US nowadays. Guess I was mistaken if a DEFENDANT can get a gun into a courtroom!
In general, in Wisconsin courtrooms bailiffs are unarmed. Their usual purpose is to escort the jury back & forth from the jury room, to & from meals, etc. Court security officers (deputy sheriffs) who bring the defendant to & from jail aren't armed--unarmed because arms are not allowed in areas where prisoners are housed (in this case, the defendant would be in a holding cell) because those weapons could be used against them. OTOH, other court security officers (deputy sheriffs) in the courtroom are armed. At the verdict in murder trials, I've seen anywhere from three to twelve armed deputies in the courtroom on both sides of the bar, plus one to four in plain clothes. Usually two to four armed deputies are stationed in a line directly behind the defense counsel table. My guess is the now-dead guy grabbed the gun from one of those guys, but didn't have much time to use it before the detective plugged him.