WALTHAM (CBS) — The City of Waltham is offering a $5,000 reward for information leading to an arrest of a person or people behind at least 10 random, unprovoked attacks that have occurred in the city since Nov. 10. Police announced the reward at a press conference Tuesday morning.

“One of the reasons for the reward is you know someone’s struck in the head with a blunt object. This strike alone could cause a serious head injury as put a fall to the pavement,” said Police Chief Keith MacPherson. “There’s definitely the potential for serious injury or even death for this type of assault.”

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The most recent attack was on Nov. 27.

Police said they have increased patrols in the downtown area with officers in uniform and plain clothes. The department is also using a drone to expand their search. The drone could potentially track the suspect if it caught an attack happening.

Police are looking for this man in a series of attacks in Waltham. (Image credit: Waltham Police)

Detective Sergeant Steve McCarthy said there are some persons of interest.

“We have gotten some, some tips, some leads to our anonymous tip line which we’re pouring through now trying to get more information on the suspect. But as to this point right now we do not have a specific suspect. We do have a couple of persons of interest that we are looking into,” he said.

Victims have a limited description of their attacker because they approach from behind and then run away immediately. MacPherson said the suspect has been described as a Black man between 5’5″ and 6′ tall, either wearing a mask or a hoodie pulled tightly around his face.

“The motive is somewhat in question but it appears to be a thrill of the assault or someone who’s like very violent and enjoys seeing someone hurt by this,” said MacPherson.

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“These incidents aren’t occurring in a vacuum, the suspect or suspects are sharing the information with people they’re close to. So, we think it at the very least, that those close to them will be aware of it,” he added.

The victims are all men but range in age and race. None have been robbed. The men may have appeared distracted.

Police are looking for this man in a series of attacks in Waltham. (Image credit: Waltham Police)

Last week, police released surveillance video of a suspect. They said Tuesday it is still the only surveillance video they have of the suspect at this time.

The first two attacks occurred on Middlesex Cir., followed by three on Middlesex Road, then one Chestnut St at Lowell St., one on Charles St at Prospect St., two in the Charles St. area, an unconfirmed attack on Hall St. and an attack most recently Chestnut St.

Waltham residents are on high alert.

“Now I look at every person that I’m walking by like could this be the person,” said Mike Cohen.

“My housemates and I certainly make sure we lock our doors now,” said Dawson McNamara-Bloom.

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Anyone with information is asked to call Waltham Police at 781-314-3600 or at their anonymous tip line, 781-314-3636.