"Detectives believe the odour came from a broken glass vial containing a clear clear liquid giving off a 'rotten egg' smell,"
From high school chemistry class, butyric acid springs to mind. Nasty rotten egg smell. They would use it in VERY small amounts while conducting diffusion experiments. You could smell it from fifty feet away about two seconds after the top was off the bottle.
Butyric acid odor is actually that of rancid butter...truly horrible. Hyrodgen sulfide is the rotten egg odor.