CAMBRIDGE (CBS) – Police are investigating a pair of violent assaults within 15 minutes of each other in Cambridge’s Harvard Square late Saturday night.

Around 10:30 p.m. a man was crossing Eliot Street at Bennett Street when he was approached from behind.

The victim was grabbed and stabbed in the back of the head. He suffered a non-life threatening injury and was taken to an area hospital for treatment.

Police say the suspect was with two other people when the incident happened.

About 15 minutes later, an Arlington man who was leaving work and walking toward JFK Park was stabbed in the back and punched in the face by a man who was with a group of three other people.

The second victim refused medical attention.

“It is such a heavily trafficked area, and there are people here at all times of the night so it is really surprising,” said one woman.

Cambridge Police described the suspect in both attacks as a black man about 6-feet tall with a medium build.

In the first attack, the suspect was described as having afro-style hair.

“I wouldn’t presume that this is necessarily crime, it could be somebody that is mentally unstable,” said Cambridge resident Temple Fennell. “We all have to be thoughtful and mindful of our own safeness and our friends, and family and even our strangers, that we are in the community with.”

Police are not sure what weapon was used in either attack.

Anyone with information is asked to call Cambridge Police at (617) 349-3300.