I think it is a bad omen to do so. I firmly believe That place is haunted or a center of paranormal activity. In light of recent deaths that were freakish accidents in nature.
If you don't believe something is odd with that site, would you consider buying a house where lets say, 10 people were brutally murdered and then burned? Chances are the answer would be "no". So why build on a site where thousands had died tragically? There is a house near me where a dude committed suicide, and the house has been sold three times in a short period of time, coincidence, I think not.
They need to just pave it over and put a monument on it, or build a park. If they build a building on that site, (that is if they can, because for some reason, things have been going slow), there will be more freakish things happening.