...who's lobbying quite specifically did not help prevent hundreds of deaths
Actually, it probably
prevented a damn sight more deaths. Places that have concealed carry & castle doctrine have drastically lower rates of violent crime than those that don't. What has Chicago's handgun ban given them? One of the highest murder rates in the US.
If you're trying to pin the Colombine deaths on Heston, then I'd suggest that had his lobbying been more successful (i.e. to the extent that the teachers were allowed to carry), then there would have been fewer deaths in that tragic incident.
Bottom line: criminals don't care about laws banning firearms, but they do care about a potential victim shooting back.