Andrew Graham died from a single gunshot to his torso during a mysterious confrontation in his quiet Centennial neighborhood early Friday morning, the Arapahoe County coroner said Monday.The 23-year-old CU graduate student's body was found on a residential lawn less than a mile from his parent's home. Investigators believe he was walking home when some sort of confrontation occurred."Mr. Graham died from severe internal injuries due to a gunshot wound to his trunk. It was just a single gunshot wound," said the coroner, Dr. Michael Dobersen, who conducted the autopsy Monday morning. "I'm ruling the death a homicide."Dobersen declined to specify whether the victim was shot in the front or back, citing the need to protect the ongoing investigation.Investigators said Graham was apparently shot to death in a random attack, which makes solving the case more challenging. Initially, authorities said Graham's body had no visible trauma injuries. "Right now, it would appear to us to be a random encounter that turned into some type of conflict," Arapahoe County Sheriff Grayson Robinson said. "Certainly, that makes it a bit more challenging and more important that the community comes forward with information they might have about this tragedy." The sheriff said there are no known suspects and there were no reports of anyone fleeing the shooting scene. "We have a videotape of him walking off of the light rail station (at Interstate 25 and County Line Road) at 11:40 on Thursday evening," Robinson said. Graham, who did not have a car and used public transportation, had spent Thursday night in Boulder looking to lease a home with friends. He was planning to go back to school there to pursue a graduate degree in civil engineering. The sheriff may make the videotape public as soon as Tuesday to encourage potential witnesses seen leaving the station with Graham to contact authorities. "We do not believe in any way, shape or form that these people are responsible for his death," Robinson stressed. But, as potential witnesses, they could shed light on what happened to Graham. The young man's mother pleaded for the public's help in solving her son's killing."He had such as life ahead of him. I wish that I was half the person he was," said Cyndi Graham, the victim's mother. "So please, anyone who knows anything please, please call us and let us know." CU-Boulder officials also mourned Graham's senseless death. "On behalf of our entire university community, I want to express my condolences to the family and friends of CU alumnus and soon-to-be graduate student Andrew Graham, who was the victim of a random homicide," Chancellor Philip P. DiStefano said in a Monday statement. "It is difficult to lose any member of our CU family, but to lose such a promising young person to an act of senseless violence strikes at the heart and soul of our community," DiStefano added. "Andrew's death is a call to us to rededicate ourselves to eradicating violence from our midst, and to continue our research and teaching to achieve that end." Robinson said investigators found Graham's satchel a few blocks from his body with nothing missing, including passport, cash, credit cards and identification. Robinson said Graham was the type of man who would walk away from a fight, but rush to help anyone in need."He was a man with purpose and he was a man with a very, very promising future in life. It is outrageous that that purpose and that promise has been taken," said Robinson.He said there is now a sizeable cash reward for anyone with information on the crime.