An official-looking prank letter telling students to attend a mandatory “vagina inspection” in the gym at Prior Lake High School has parents, students and teachers wondering whodunit.

No one knows exactly who is behind the letters, written on imitation school letterhead and hand-delivered to some families’ mailboxes this week.

Nor do they know how many were sent out, but the Post Office took notice and removed 50 letters, said Kristi Mussman, district spokeswoman.

An image of the letter was shared widely on Twitter and other social media as well and was a “topic of conversation” at the high school Tuesday, Mussman said.

“It’s definitely a hoax. We believe a student or students created it after school hours,” Mussman said.

After the school’s police liaison officer saw a tweet about it on Tuesday, Principal Dave Lund sent out an e-mail to parents explaining that administrators “are aware of this letter and we are addressing the issue internally.”

Mussman said the prank was “done in extremely poor taste” and administrators were “disappointed.”

Right now, determining who wrote the letter is a police matter. The liaison officer has “some strong leads” so far, she said.

Because there is no evidence that it was written at school or printed on school property, administrators aren’t sure whether they could punish the offender, should they discover the person’s identity, or what that punishment might be, she said.

“I’m sure there have been pranks [here] in the past,” Mussman said. “This is obviously one of the bigger ones.”