The man was apparently an Art dealer. Did he keep it in the Apartment? What kind of art reeks of sulfur? Perhaps he dabbled in Chemistry on the side! Sulfur in Art conservation.
http://resources.conservation-us.org/wp-content/uploads/sites/8/2015/02/osg019-05.pdf
Was he trying to burn some kind of creepy evidence?
The plot thickens...
4. Rotten Eggs (SULPHUR SMELL)
The smell of rotten eggs is instantly recognizable, and can be an indicator of a serious problem in your home. The two most common sources of a rotten egg smell are a natural gas leak, and escaping sewer gas.
In its natural state, natural gas is actually odorless. That’s why utility companies inject a substance called mercaptan, which emits an odor that smells like sulfur or rotten eggs. If there’s a very strong smell, you could have a substantial natural gas leak. Leave the area, call 911 from a safe place, and call your utility company so they can send out a technician as well. It’s also important not to smoke or use matches or lighters, because natural gas is flammable.
If you detect a faint smell of rotten eggs on occasion, you may have a leak of sewer gas, which contains toxic elements including hydrogen sulfide and methane. Often the source of sewer gas is a bathroom that isn’t used very often. The pipes under a shower or sink have a u-shaped trap where water usually blocks sewer gas from leaking back into a home. To create that barrier, simply pour a cup of water into the bathroom drain. If you can’t find the source of the sewer gas leak in your plumbing, the issue could be a vent pipe, which disperses sewer gas through a home’s roof. If you can’t find the source, simply call a home inspector or plumber to investigate.
http://stormguardrestoration.com/top-five-smells-concerned-home/