He was one of the most famous musicians in history, and for a time, he was one of New York's most famous residents.
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He was gunned down in front of his home on the Upper West Side in a murder hat shocked the world.
Fellow Beatle Paul McCartney called the anniversary a "sad day," but remembered the joy his former bandmate brought to the world.
Fans across New York City spent the day remembering his legacy.
"John Lennon is my idol, he is the one who made me want to pick up a guitar," said musician Christian Estrella.
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They came for all different reasons - some for his music and some for his message.
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"His aspiration was to have a better world," fan Clara Tello said.
At Strawberry Fields on Tuesday they remembered Lennon with candles, flowers, pins and songs.
The Imagine mosaic was filled with mementos -- all just across the street from the Dakota: the building where Lennon lived and where he was killed 40 years ago.
Roger Quinton came to the site the day after Lennon died 40 years ago to pay his respects and mourn. He returned on Tuesday to do the same.
"It just felt good to come back and remember him," Quinton said. "He stood for love actually. He went through bad times and managed to survive them and I think that's what we all do."
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Lennon was a man so famous, and yet, still a man of the people, who was killed by a crazed fan who remains in prison.
But Lennon's legacy lives on.
"It's insane how much time has passed and people still gather to celebrate him, it's so beautiful," Madison Leonard said. "I feel like he is here spiritually. I really wish he were here, I really do wish he were here."
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