By Emily Opilo From The Baltimore Sun Baltimore Police are investigating a shooting that killed three men and injured a fourth in Northwest Baltimore on Saturday night. At approximately 8:20 p.m., police were called to the intersection of Gwynn Oak Avenue and Liberty Heights Avenue in Howard Park. When officers arrived, they saw four men inside a vehicle, all suffering from gunshot wounds. Three of the men were unresponsive and pronounced dead after arriving at the hospital. All three were 25 or 26 years old. The fourth man, who is 73, was transported to the hospital with non-life-threatening injuries. Nearly two dozen evidence-markers dotted the sidewalk across the street from a Shop Rite grocery store. An SUV, still running and with its doors slung open, sat in the middle of Gwynn Oak Avenue. About an hour later, police say, a man was shot in the 2200 block of West Patapsco …