It’s a mystery that Nassau police would like the public to help solve — the identity of a man found dead in October at a county park, a YMCA of Glen Cove backpack and a mountain bike nearby.

He appeared to be about 40 years old, 5 feet, 2 inches tall and 121 pounds, with black hair, brown eyes and a light mustache and beard, police said.

He was found about 12:50 p.m. Oct. 6 at Cantigue Park on West John Street in Hicksville, police said.

He had on a black Koppen brand windbreaker and a Gilden brand blue T-shirt with “Soccer for Community” and “Gosports.com”; the word “Staff” was on the back, police said. He wore black BBC jeans, navy Jockey shorts, tan American Connection boxer underpants, black Adidas socks and tan Mephisto leather shoes, police said.

He also wore a black Forty Seven brand baseball cap with the NY Yankees logo, police said.

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His backpack contained three empty, pint-size bottles of Georgio vodka and some clothing items, authorities said.

Police ask anyone with information to call Crime Stoppers at 800-244-TIPS (8477) or the police missing person squad at 516-573-7347.