The Wisconsin State Journal reports. What was he doing? I think I understand:

Shorewood Hills Police Chief Aaron Chapin said Jonathan M. Fitzgerald, 35, activated a front door buzzer at the school, 1105 Shorewood Blvd., around 10 a.m., requesting access to the building. When he was allowed in, he walked past the school office where visitors are required to check in, Chapin said.

A staff member followed Fitzgerald as he went down the hall to the classroom his child was in, Chapin said. “Fitzgerald made statements to the teacher in the room about being an intruder who was allowed access to the school and gave the teacher a piece of cardboard with the word ‘gun’ on it,” Chapin said.

Chapin said Fitzgerald left the classroom and went to the administrative office where he made similar statements and handed staff another piece of cardboard with “gun” written on it, then left the school building.

Based only on those facts, I would assume that he was trying to demonstrate that the children are not safe, that a person with an actual gun would not have been stopped.

He was arrested. On what charge? Disorderly conduct. That is defined in the Wisconsin statutes as "violent, abusive, indecent, profane, boisterous, unreasonably loud or otherwise disorderly conduct under circumstances in which the conduct tends to cause or provoke a disturbance." The statute goes on to specifically provide that "a person is not in violation of, and may not be charged with a violation of, this section for loading a firearm, or for carrying or going armed with a firearm or a knife, without regard to whether the firearm is loaded or the firearm or the knife is concealed or openly carried." But, of course, a piece of cardboard with the word "gun" written on it is not a firearm.

ADDED: Meanwhile, in Allen Parish, Louisiana, they got a search warrant against teenager who made a comment about the way the square root symbol looks like a gun.

"The students were working together, and a student made a math symbol of a square root sign, which kind of looks like a pistol. And he was helping a weaker student, and the student says, 'Well, that looks like a pistol!' And he just made a comment [like] 'let's just get to work before I shoot you with a pistol,” said Superintendent Doucet.

Gossip turned it into a rumor about the student plotting to carry out a mass shooting at Oberlin High School. The rumor warranted a search of the student's home for guns.