The teen was able to block the door long enough to allow his classmates to escape through a back exit, CNN reported. Garcia's aunt, Sarah Saunders, told KHOU that her nephew "died a true hero."
“He laid down his life so others could have a chance,” Saunders told the news station. “He had the biggest heart and the biggest chunk of ours feels to have left with him.”
Smith, who baptized Garcia, described the teen as "a fun-loving kid who loved playing football and enjoyed being outdoors," CNN reported.
"That's not what's supposed to happen to a 15-year-old's life, that he has to make those decisions," Smith told CNN. "But he made them without even thinking about it, because it was his heart. This is who he was as an individual."
Family members told KHOU that Garcia wanted to enlist in the military after high school because he "felt it was his calling to serve others."
Seven other students and two teachers were killed Friday in the shooting at Santa Fe High School. The alleged shooter, 17-year-old Dimitrios Pagourtzis, faces multiple capital murder charges.
WATCH: Victims of Santa Fe High School Shooting