(CNN) Staci Martin took many pictures during her first trip to London this past week, but there's one she'll never forget.

Curious about the police officer standing guard outside the Houses of Parliament in Westminster, Martin asked for a photograph with him. Soon after, the area would be engulfed in horror, and Keith Palmer, the 48-year-old police officer who smiled politely for her photograph would be dead.

Martin, who is from West Palm Beach, Florida, traveled to London to visit her son who is studying abroad. While taking a tour of the city, her son showed her Parliament. Martin spotted an officer and was intrigued by his hat, so she asked to take a photo.

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"I asked the officer if a photo was OK," Martin told CNN. "He said yes, and I asked him if this happens a lot. He told me, 'It happens quite a bit.'"

She and her family left to eat lunch a block away. When they were leaving the lunch, the attack happened. The family didn't see the attack.

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