On Sunday, ABC13 learned that the suspect was wanted for murder out of Louisiana.
Investigators said the stranger saw the robbery as it was happening at a Chase Bank in the 10400 block of Westheimer Road.
A man pulled into the bank to withdraw money from the ATM when the armed suspect came around the corner and ordered him to hand over money, according to police.
Detectives said the victim reportedly began to comply until the suspect began to pistol-whip him.
That's when police say someone driving by saw the crime happening and pulled out a gun to defend the victim.
The man shot the suspect in the leg and foot after several shots were fired. The suspect was taken to the hospital in stable condition, according to Houston police.
Investigators interviewed the victim and passersby, who were not harmed.
According to ABC13's Safety Tracker, in the zip code where the incident happened, 77042, there have been at least 103 robberies in the area in the last year.
Eyewitness News is still working to get details on the circumstances around the suspect's murder charge.
For more news updates, follow Courtney Carpenter on Facebook, Twitter and Instagram.