This is more like 2 questions and 12 related points than a single "counter question," but okay.
Why does it have to be Rum who's using Kogoro to try and find the uploader? A rival of Rum's within the BO would be just as interested in a big mistake from his past. A chance to show up Rum and gain the Boss' favor and approval, and all at Rum's expense? A rival of Rum's definitely wouldn't pass such an opportunity up.
For all we know—whether Kanenori is Rum or another high-ranking BO member—the Boss didn't authorize Kanenori to go investigate Kogoro. This could be a completely independent effort, on his part—either to clean up his 17-year-old mistake... or to do what his rival, Rum, couldn't, to show him up, and show the Boss who is really worthy.