 Brian was able to slip Joe a sedative, and then injected him with insulin, causing Joe to have a seizure and die of cardiac arrest.When Dexter, Rita, Debra (Dexter's adoptive sister) and "Rudy" came to sort out Joe's house, Dexter took blood samples of himself and Joe and sent them to Vince Masuka to perform a DNA test, which came back as a match.Dexter suspected that Joe's apparent heart attack was actually murder.