Deputies say Judas Deluna, 21, got into an argument near the taco stand in the parking lot just after 6:30 p.m.
Surveillance video shows Deluna go to his vehicle, grab a gun and open fire, shooting the first victim several times.
Two bystanders came to the victim's aid and, according to deputies, Deluna fired several shots at the men.
"As he was going outside he saw the injured guy, so he took his phone out to call an ambulance so somebody could come and get him to make sure he was fine," Rupani's sister Muniza Kabani said.
Rahman Rupani and the other bystander were both shot.
Rupani died at the hospital. He was just trying to help another man who had been shot outside.
"Trying to help everyone and be welcome to everyone, I don't know why they would do that," said Victor Ibarra.
The first victim and second bystander are in stable condition at the hospital.
On Saturday, flowers and balloons could be seen outside DJ's Food Mart. Frequent customers told ABC13 that it will never be the same.
"He died a hero, protecting people he has no duty to protect," Rupani's younger brother Karim Rupani said.
Deputies say Deluna and two other men fled the scene in a black Lincoln Navigator.
The Navigator was found abandoned near Antoine and West Greens roads. Investigators were able to trace it back to Deluna.
Deluna has been charged with murder.
Captain Joe Ambriz with the Harris County Sheriff's Office said, "I'd like to make a plea to the public that if they saw anything or heard anything, if they were in this area of Bammel North Houston that they call the Harris County Sheriff's Office."
Anyone with information about his whereabouts is urged to call the HCSO Homicide Unit at 713-274-9100 or Crime Stoppers at 713-222-8477.
"We need to find this guy. We just need closure,"Karim Rupani said. "Help us out."
Deputies warn that Deluna should be considered armed and dangerous.
"Whoever did that, they should pay for it," added Ibarra.
Rupani leaves behind a wife, 6-month-old and a 2-year-old.
New surveillance video released of suspects wanted in fatal shooting outside northwest Harris Co. store