Assuming the cops aren’t incompetent and/or utterly corrupt, they should determine rather quickly whether anyone else was involved. If someone killed him in the bathroom it would have been very difficult to do so without leaving evidence of some sort. The cops dusted for fingerprints, but even if an attacker had gloves on there would have been something…shoe prints, blood smears, hairs etc. And Tony says there are cameras all around the outside of his house, as well as his neighbors houses, so by reviewing that footage it will be very easy to determine who was in the house around the time of death.