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Lowe said police received a call from someone reporting hearing up to seven shots fired in the medical office. Police arrived and found both the gunman and the shooting victim in the office.
The gunman, a man in his 70s whose name was not immediately released, was arrested without a struggle. An employee who works in the building said the gunman had a scheduled appointment with the slain doctor.
Police did not identify the person who was shot, but witnesses told NBC4 that the man was possibly a urologist.
Because the building is so new, witnesses initially thought the shooting was the sound of construction.
"I thought it was construction, like a nail gun," said Kristin Crotty, an employee at the medical facility.
The doctor has a wife and two children. His family declined to comment late Monday.