A doctor who was shot at Brigham and Women’s Hospital in Boston succumbed to injuries late Tuesday night, according to local police. The victim was identified by police as Dr. Michael J. Davidson.

The incident took place after the gunman, later identified as Stephen Pasceri, entered the hospital on Tuesday morning and asked for Davidson. The 55-year-old man shot the doctor and was later found dead, with what police believed were “self-inflicted gunshot wound.”

“There’s something in the past that upset this guy to come in looking for this particular doctor,” Police Commissioner William Evans said, at a press conference, according to Boston.com.

A preliminary investigation into the shooting suggested that the gunman had “some issue” with a previous medical treatment his mother underwent at the hospital, Boston Globe reported, citing the head of the Bureau of Investigation Services. Pasceri’s mother reportedly died on Nov. 15.

“Investigators believe that at some point during his meeting with that doctor, Pasceri produced a firearm and shot the victim,” Boston Police Department said in a statement.

Police Commissioner William B. Evans reportedly said that the motive of the shooting was unclear and an investigation was underway.

“There was a particular reason he targeted this doctor,” Evans reportedly said, calling the incident an “unfortunate tragedy.”

Davidson was working as a cardiac surgeon at the hospital since 2006 and was also an assistant professor at Harvard Medical School.

“We had a very tragic situation here this morning,’’ Dr. Elizabeth Nabel, the hospital’s president said, in a statement. “Our hearts go out to the victims and the family members. All affected, including our staff, are in our thoughts and prayers. These are very, very difficult situations and it can often take a while to really recover from them.”