Catalano reported that last year alone HUPD responded to 53 reports of harassing phone calls, but that an estimated 50 additional complaints about harassing calls are instead classified as “suspicious activity.” On average, Catalano said, approximately a hundred harassing or suspicious phone calls are reported to the police department each year.

Catalano refused to speculate on whether the recent spate of calls could be related to these previous complaints.

In October 2003 and December 2004, students complained about “sexually provocative” phone calls made early in the morning by a “whispering” caller.

In November 2001, HUPD officials traced calls from a so-called “serial whisperer,” infamous for phoning female undergraduates in the early morning hours to tell them he was “crazy about you.”

Some students reportedly received up to 30 calls from the man in a two-month period. HUPD traced the calls to determine the caller’s south Florida location and worked with officials there to order the man to stop calling. Complaints subsequently declined, according to HUPD.

“In the past, there have been some instances where people have felt it has been the same caller,” Catalano said, stressing, however, that this fact “is hard to determine.”

Catalano characterized calling in the early morning and speaking in a low voice as a “tactic” rather than a trademark.

“One of the reasons people call early in the morning is when they’re waking someone up out of bed, they’re groggy, so it’s a little harder to tell who it is,” Catalano said. “The early morning call, the caller will often whisper.”

“If I call you in the morning, I’m going to get you off guard,” Catalano said, describing the whisperer mentality.

—Jonathan P. Gordon, Chaz C. Kelsh, and Beth Pedersen contributing to the reporting of this story.

—Staff writer Samuel C. Scott can be reached at sscott@fas.harvard.edu.