Because you first heard about this story on a questionable website rather than the Chicago or Washington papers it makes it less credible? Tell that to the four dead people.
Oh, I don't even hear his explanation for how the website is "questionable." I would challenge him right now to comb through the info on that site - which is a priceless source on this subject, by the way - and explain exactly how their facts are in error.
Then when he can't, tell him to take his "guilt by association" intellectual laziness over to Salon or DU.