Mass shootings are terrible, harrowing, horrifying affairs, and yet sometimes they give rise to the most astonishing feats of bravery and heroism imaginable:

A retired police officer who worked as a security guard at the Buffalo supermarket where a gunman shot and killed 10 people Saturday was hailed for his bravery, with officials saying his actions before he was struck down likely saved the lives of others.

Aaron Salter Jr., who worked on the Buffalo Police Department for decades before retiring several years ago, according to the Buffalo News, confronted the suspected gunman inside Tops Friendly Markets, officials said. Salter's shots failed to penetrate the armored vest of the suspected gunman, later identified as 18-year-old Payton Gendron, and the gunman returned fire, killing Salter.

"He's a true hero, and we don't know what he prevented. There could have been more victims if not for his actions. He's been retired for several years. He's been a beloved member and employee of Tops here, working security and he went down fighting," Buffalo Police Commissioner Joseph Gramaglia said on ABC's "This Week." "We're sure he saved lives yesterday."

That's a hero's death.

Salter's colleagues, meanwhile, were unsurprised by his last full measure of devotion:

"It's not surprising to me, at all, that he did what he did yesterday," said retired Lt. Steven Malkowski, who previously served as Salter's supervisor when they both worked in the Buffalo Police Department's Traffic Division. "Even though you leave the job, the job doesn't leave you. I know he was thinking about, something was going wrong here. People's lives were in danger, and he was probably the only person who was in there that could help and save people."

Amazingly, in addition to having an obvious hero's disposition, this fellow also had astonishing plans to change the world:

What his friends and colleagues remember most about Salter is his interest as an amateur scientist to create the world's first car engine that could run on water. The engine would break down water, separating the oxygen and hydrogen molecules so that they would be used to power the vehicle. He even had detailed drawings of his invention.

It's a terrible loss on top of every other life taken that day. May swift justice be done for all of them.

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