The latest info I found is this story:
http://www.madison.com/wsj/mad/top/i...hp?ntid=269886
The 8-inch knife was found in the livingroom. So unless it was from his own kitchen, most likely someone knocked on his door, forced their way in and stabbed him during an altercation. If it's from his own kitchen, it may be someone entered the home thru stealth, obtained the knife and then used it when confronted by the victim.
The paper noted police collected a pair of rubber gloves from the front porch. These may have been discarded by the killer as he left and if so, I suspect he broke in quietly, armed himself and killed the resident when confronted.
Note that burglary convicts have said that they prefer to enter near a kitchen so they can obtain a knife in case they meet an occupant. If the job goes smoothly, they can drop the knife back in the drawer and exit "unarmed" in case the cops catch them.