About half of the students at Liberty High School chose not to attend classes Wednesday, because of a four-month-old threat.

A janitor found a note scribbled in pencil on the boy’s bathroom wall in late June that said the writer planned to “shoot everybody” Oct. 27.

The King County Sheriff’s Office didn’t find a suspect over the summer, and the note continued to make parents uneasy.

“These generalized threats, especially in a bathroom written on a school wall, are relatively common,” said King County Sheriff’s Sgt. John Urquhart. “It usually happens the day before a math test.”

Police take the messages much more seriously when students start writing hit lists or are specific in their plans, he said.

Despite about 550 of the 1,100 students not attending classes, the school went on without incident.

The district reported that the students that did attend had a productive day. Showing his support, Superintendent Steve Rasmussen strolled the halls and dropped in on classes.

A school resource officer was at the Liberty, but there wasn’t an unusual presence of police.

The week before, the school principal sent families an e-mail explaining how the staff planned to “increase awareness” but still remain open.

“Even as we operate under the best safety advice from experts, I understand how you may be personally questioning whether or not your student should attend school on that day,” Principal Mike Deletis wrote. “I want you to make the decision that is right for your family.”