A Chicago police officer and two hospital workers were killed Monday by a gunman who carried out a grisly assault at a city hospital. Police identified the fallen officer as Samuel Jimenez, a young cop with less than two years with the department. Hospital officials said emergency room doctor Tamara O'Neal and first-year pharmacy resident Dayna Less were the other victims in the afternoon shooting at Mercy Hospital on the city's South Side. The shooter, who authorities identified as 32-year-old Juan Lopez, also was killed in the incident. He was previously engaged to O'Neal, according to family members who spoke with reporters.