A man's body was found underneath the old Holbeck viaduct, off Whitehall Road, this morning. The structure has been derelict since the late 1980s.
Police scene of crime officers are currently at the scene.
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A surveyor assessing the viaduct site for future development discovered the man just after 11.30am today and asked Mohammed Maroof, the head of security at nearby office building Number One Leeds, to help check on the man's welfare.
"He called me over as I have a key to the site and we both had a look around. He was lying at the back of an arch and we both shouted to him, but he didn't respond. We were scared to get too close - we could see his skin was really pale. We called an ambulance and waited for the paramedics, who said straight away that he was dead.
"He hadn't moved at all in about half an hour. The police came and sealed it off.
"He didn't look like a homeless person or someone who'd been sleeping rough. There was lots of blood around the arch and on the bricks. He didn't have a blanket or any covering but there was a jacket that had been left on the edge of the archway. It was hard to tell his age.
"I'm really shocked - I've been in security for 19 years and never seen anything like this. The police said they'd keep me updated."
The viaduct - which used to carry a railway line from Farnley into a now-demolished station just off Wellington Street - is currently the subject of a development scheme which could see the arches become shops, cafes and bars. Surveying work began several months ago.
The arches were also used for the filming of a BBC adaptation of Agatha Christie's Poirot novel The ABC Murders in July. Extras in 1930s police uniforms were seen close to the spot where the body was found. The drama is due to be screened this Christmas.