I really do doubt he restrained himself to those four in such a limited window of time. It would be highly unusual for this type of offender.
I still think we're dealing with someone with a higher body count, a longer window of killing. If he's definitively not responsible for the other LISK cases, they should be looking somewhere else in his orbit for victims. Somewhere he worked, travelled for business or pleasure, lived for a period of his life, studied (architects need a degree), etc. They should be looking for survivors, people who escaped him. I only hope that they do the deepest of dives into every dark corner and secret of his life and find where they need to look for those others. They and their families deserve justice, too.
MOO