Business owner nearby Susan Jimenez - no relation of Samuel - said she heard multiple gunshots with pauses in between.
The hospital identified the slain staff members as 38-year-old Tamara O'Neal, an emergency room physician who never worked on Sunday because of her religious faith, and Dayna Less, 25, a first-year pharmacy resident who had recently graduated from Purdue University. And Officer Samuel Jimenez had been a Chicago police officer for less than two years and was the loving father of three young children. "She asked us not to leave her alone because he is going to kill her".
Dr Patrick Connor, director of the Mercy Hospital's emergency department, said Dr O'Neal was "dedicated to caring for her community - a wonderful individual".
The scene outside Mercy Hospital. Both of the women were taken to other hospitals nearby.
There are "reports of multiple victims", police say - but they have not given a number or said how severe the injuries are. He then entered the hospital and fired the shots that killed a pharmaceutical assistant and a police officer.
The shooter was also fatally wounded, but it remains unclear whether or not the wound was self-inflicted, Johnson said.
He said one of the women killed was in a domestic relationship with the gunman. He added: "This just tears at the soul of our city".
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"Every shooting in America is a tragedy, and it is especially senseless when a shooting occurs in the healing space of a hospital", the statement said. It is the face and the effect of evil'.
Vallon K. Stefferson, 27, was walking down the 13300 block of South Langley Avenue just before 10 p.m. when he was approached by three people who fired shots, according to Chicago police and the Cook County medical examiner's office.
"She said 'I love you.' That's the last words she spoke to me", Thomas O'Neal told ABC Chicago station WLS-TV. The two argued because sources say O'Neal broke off the engagement.
"It was just nothing but pow-pow-pow", she said. She later started a blog with her mother called "My Daughter's Headache" in an attempt to help others with the same condition find hope.
Mercy Hospital held its first-ever active shooter drill just weeks before the shooting Monday that left four people dead - a move that might have prevented even worse carnage, hospital officials said. She looked down and saw blood on the floor but no bodies.
CBS Chicago learned that O'Neal studied at the University of IL in Chicago before working in Mercy Hospital's emergency room.
"It may have been 15 minutes, but it seemed like an eternity", she told a reporter. "And I am extremely grateful to the Chicago Police Department who responded with bravery", Durbin said via Twitter on Monday.