David Nixon's missing person's case file never leaves Det. David Brady's desk.

It's a 30-year-old cold case the detective has been working on for several years — but he just can't let it go. "His file is never put away in a drawer. It's always there," Brady told CBC Hamilton. "This has haunted me my whole career."

"I know someone knows something."

It’s not rare for police to turn to the public for help to find a missing person – but making a concerted effort to find a man who disappeared in 1984 is much less common. But Brady is doing just that, and asking for the public’s help in tracking down a man who went missing 30 years ago to the day this Sunday.

Police say this sketch shows what David Nixon might look like in his 40s. (Hamilton Police)

After speaking with his mother, Nixon was last seen by his uncle on the corner of King and James in Hamilton on July 6, 1984. On that summer day, Nixon’s uncle invited him for coffee but he declined, and said he was running late to meet someone else.

He then walked westbound on King Street West from James Street. He wasn’t seen again. Brady says he's appealing to the public decades later because he feels like he has a duty to give Nixon's parents — now in their late 70s — some peace of mind. "I've got two elderly parents here and the best gift I could give is resolving this," he said. Nixon had no criminal background and was religious, Brady says. "This was a young man who was very close with his family. It's very uncharacteristic."

"There's no way somebody doesn't know something. Maybe someone from back then now has children of their own, and they'd think differently about coming forward."

Brady says that Nixon left the city unexpectedly once before to visit British Columbia, and there was some speculation at the time of his disappearance that he may have gone to England to visit a woman he’d been exchanging letters with. "There was a friendship there, and I think that's as far as that went," he said. "I don't think that's a viable option." He does concede that foul play is a possibility, considering Brady hasn't turned up in the last three decades. "It's certainly a consideration," he said. "And it's the most logical explanation — but we have nothing conclusive that would point us to that."

Nixon was 24 when he disappeared, and would be 53 years old today. He is described as white, about five foot ten, 150 pounds with a medium build with light brown, short curly hair and blue eyes.

Anyone with information about Nixon or his whereabouts is asked to call police at 905-546-3873 or Crime Stoppers at 1-800-222-8477.