Barry Fitzpatrick, the principal of Mount St. Joseph High School, resigned Tuesday after officials there discovered "inappropriate" communications with students, the school said in a letter to parents.
The school did not detail the content or the type of communications but said the "proper authorities" had been notified, school president George E. Andrews Jr. wrote in the letter obtained by The Baltimore Sun.
Baltimore police spokesman Anthony Guglielmi said he could neither confirm nor deny an investigation.
Fitzpatrick could not immediately be reached for comment Wednesday.
Mount St. Joseph, a private all-boys school known for its athletics, has had a turbulent couple of years. In December 2011, its longtime president, Brother James Kelly, died of prostate cancer.
"Our Mount Saint Joseph family has weathered a number of difficult days over the course of our 137-year history. Today is such a day," Andrews wrote in the letter.
"Our students mean everything to us. … As such, we have the highest expectations for our faculty and administrators. And when these standards are not met, we have a responsibility to our boys and their families to take action," the letter continued.
Andrews could not be reached to comment and did not respond to emailed questions. His assistant said he was fielding questions from parents by phone Wednesday afternoon.
Fitzpatrick had been principal at the school in Baltimore's Irvington neighborhood since 1994, according to a biography that has been removed from the school's website. He started at Mount St. Joseph as a guidance counselor in 1986 and was known as "Mr. Fitz" to students.
Raised in Brooklyn, N.Y., Fitzpatrick studied at Catholic University in Washington, D.C., as well as Loyola and Harvard universities.
"He's an avid sports fan and a voracious reader," the biography reads. "But his true love will always be his students."
Don Kemp Jr., a 1978 graduate of the school and a member of its board, said directors had not been told anything more than what has been made public about Fitzpatrick's resignation. The board, which will have to approve Fitzpatrick's replacement, will gather Friday for a scheduled meeting, he said, and will likely find out more then.
Kemp said Kelly and Fitzpatrick helped pull the school out of a "period of stagnation" during which its "leadership wasn't quite up to par." The loss of the school's two top figures in such a short space of time will be a blow, he said.
"He was critical to the success of the school. The school had really increased ... the quality of the experience for the boys, educationally and otherwise," Kemp said.
Director of studies David Norton will serve as acting principal until Fitzpatrick is formally replaced.
Ryan Dice, 18, who graduated from Mount St. Joseph last year, said Fitzpatrick played an especially big role after the death of Kelly. He led prayers and assemblies, and encouraged students to remember Kelly, Dice said.
"Mr. Fitz really brought the school together. That's why a lot of people liked him," he added.