(CNN)Eleven unprovoked attacks have occurred in the last month in a Massachusetts city, scaring residents and confounding police.
Now, the Waltham Police Department is asking for the public's help. The department released footage of a person in a hoodie, their face obscured, who police say is a suspect.
The attacks began November 10. The first five occurred near an apartment complex, minutes from Bentley University, but more recent incidents have occurred downtown, Detective Sgt. Steve McCarthy told CNN.
As of last week, there have been 11 unprovoked assaults recorded in the city, McCarthy said. The victims were all targeted with a blunt object by an unknown assailant after dark, he said.
One victim, who said he was attacked the day before Thanksgiving, is in the hospital with several breaks in his face and skull, CNN Boston affiliate WCVB reported.
David Cameros, another victim, told WCVB he was hit in the eye with an unknown object before his attacker ran away.
"I don't know if it is only one or there are more attackers," Cameros told WCVB. "The aggressor always attacks from behind."
Police told WCVB they're not sure whether the same person committed all 11 assaults.
Residents who recognize the person in the video have been asked to contact Waltham police and be aware of their surroundings if they go out at night.
Waltham, about 10 miles west of Boston, has about 63,000 residents.