Merconie Clark suddenly found himself wrestling with a gunman. Darius Alston came to help.

Gunshots had just been fired in the Smith’s grocery store at East Silverado Ranch Boulevard and Maryland Parkway where Clark and Alston, who had never met each other before Tuesday, had been shopping. Police would later say that the shooter killed a woman who was the mother of his children and her current partner.

But the suspected killer didn’t get away — thanks to the bravery of several bystanders, police said. The good Samaritans who jumped into action to stop the gunman included Clark and Alston, who subdued the shooter until officers arrived.

Metropolitan Police Department Lt.…