Gibson, 27, was gunned down outside of the school where he once played center on the football team. Police say he wasn't the intended victim but appears to have been caught in crossfire.
"He was a fun, loving person," said Connie Smith, Gibson's 42-year-old stepsister, at his father's Gage Park home. "He was just someone who wanted to make something of his life."
"He just wanted to prosper in life," his father Michael Gibson added.
Gibson lived with his older brother and the two would often talk about leaving Chicago to escape the violence in their community, family said.
Morrice Gibson ultimately decided against it because he was committed to his job working with AAA's local roadside assistance team.
Before he was shot, he told his brother that he was going to take the 2.5-mile jog to Simeon to work out, family said.
"Why would he go out for a jog in this heat?" Smith said. Morrice Gibson "was trying to lose weight, so maybe that's why."
While Gibson was on the sidewalk shortly before 7:30 p.m., two shooters were aiming at a group that was standing nearby, police said.
A 2005 Simeon graduate, Gibson was caught in the crossfire and was shot in his head and stomach.
He was pronounced dead at Advocate Christ Medical Center an hour later.
"His brother called and said he wanted us to come to the hospital," said Gibson's stepmother, Emma Gibson. "His brother was shot and needed to be identified."
Smith, who returned home days before the shooting from a Air Force assignment in Laos, said she hadn't seen her baby stepbrother in over a year, though had been in constant contact with him online and via phone.
"I hadn't been able to see him since I got back," Smith said. "He was a good soul."
Smith described him as both a jokester and someone who was aware of everything. In recent Facebook posts, Gibson voiced distaste for the recent verdict in the George Zimmerman trial and the violence going on in his community.
"He was very opinionated — very engaged with what's going on in his community and world," Smith said.