So, you catch a 'thief'...

"Thing is, he had his coat, bag and helmet next to him on the floor..."

Surely this is not a bike thief. Might be fine as a decoy to you, but if the owner turns up, how is he going to leg it with his stuff lying around. He'll end up getting twatted a la Grandeanse ^up there & losing his 'decoy' stuff.

I vote genuine.

Valid point but that's the grey area. He may well have been genuine and gone back to work to fetch a set of plyers and hacksaw but I find it hard to believe that these sort of items are 'just kept at work'(unless a builder/chippy/sparky etc).
Also, as mentioned, I don't know cyclists that carry a 9/10inch set of plyers and 10/12inch hacksaw in their bag