The robbery happened at a Capital One bank on Westheimer near Chimney Rock at about 2 p.m. Police received multiple calls reporting a robbery and a shooting involving three masked gunmen.
Police say the guard's female coworker returned fire and the gunmen fled. Their white Ford F250 pickup truck has been recovered, but the suspects remain at large.
At least one witness inside the bank at the time reported hearing a gunshot, and then she says she saw a man wearing a black uniform lying on the ground.
"Only, I see the guy, he's shot and he's dead," bank customer Delilah Azzam told Eyewitness News. "I hope he is not, but I only see what I saw. I heard the gun, you know, but from where it was coming, I don't know."
The guard, identified as Alvin Kinney, 60, of Katy, was rushed to an area hospital, where he was later declared dead.