In an email to parents Wednesday, Superintendent Valerie Henning-Piedmonte said that it was Stack's "personal decision" to retire and he "will not be returning to the district."
"You should also be aware that Mr. Stack's retirement is in no way linked to the arrest of Christopher Vlangas," the email stated.
Calls and emails to Henning-Piedmonte regarding Stack's abrupt departure were not returned.
Stack's picture and contact information were removed from the school's website, and his email was no longer active by Wednesday afternoon.
Vlangas, a 41-year-old Brewster naval science instructor, was arrested Monday and charged with rape of a 16-year-old female student he is accused of having a sexual relationship.
He is being held on a $250,000 bail bond or $150,000 cash bail.
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