well, there is the chance that his vision and hearing are impaired to a point... Causing the 'slow' reaction time...
If this is the case, he actually might be the culprit.. he may not 'know'/'remember' where the litterbox is and may look for options..
you know, the clothes pile on the floor, or the papers left there as well....

try talking to him more often when he's near you.. and see if that makes a difference....