She said volunteers were informed of the rapes from newspaper articles and an e-mail from a member of the program.

“We always stress in our program that no one is allowed to walk by themselves,” Mendoza said. “We’re not happy that this happened, but we’re prepared for things like this.”

She added that she thought HUPD should have informed all students about the attacks, since many students who reside in Cambridge travel across the river for volunteer programs and other activities.

“Since all the universities are sending out notices, it would have been nice for us to hear something about it,” Mendoza said.

At Boston University (BU), campus police officers spoke to the radio station, provided information to the student newspaper about the attacks and sent a notice to the Dean of Students’ office, according to BU spokesman Colin Riley.

Northeastern University sent an e-mail alert about the crimes out to all students to “make sure that they take it seriously and take every precaution,” said spokeswoman Brylee Maxfield.

Catalano said each university makes its own decision about whether to send crime alerts.

“There is a large percentage of Northeastern students that live in Mission Hill. It is appropriate for them to warn their students,” he said. “We felt it was appropriate to warn the people who live and work in Mission Hill.”

The BPD said no arrests have been made, and the department will release a composite sketch of the suspect today.

The BPD is asking anyone with information about the crimes to call the tipline at 1-800-494-TIPS or the Sexual Assault Unit at 617-343-4400.

—Staff writer Jessica R. Rubin-Wills can be reached at rubinwil@fas.harvard.edu.