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WASHINGTON, D.C. – For the past 20 years, the mother of a slain police officer has served a holiday meal to hundreds of D.C. police officer, and this year they thanked her with a big surprise.

As Shirley Gibson pulled up to a Costco store to shop for the big meal, she was greeted by dozens of officers lining the entrance of the store.

“Oh my goodness!” Gibson said as she walked inside, clasping hand to her mouth in tears.

WRC-TV reports Gibson’s son was shot and killed on February 5, 1997 when he was just 27 years old. Every year since, she has honored his memory by feeding hundreds of his colleagues in D.C. with a home-cooked holiday meal at her home.

In November, as she prepared to cook that meal, the city of thanked her for the love she has shown for the past two decades. Metropolitan Police Officer and Mayor Muriel Browser greeted her at the Costco store and presented her with 15 tickets to the National Museum of African American History and Culture.

“She has dedicated her life since the loss of her son to helping other families who have lost lost their sons in law enforcement,” said Interim Police Chief Peter Newsham.

NBC News reports at age 70, she has decided this year will be her last year serving the meal. She said the 20 year tradition has helped her cope with the loss of her son.