I fail to see what the possible benefit to Mr Putin would be in ordering the murder of a dissident with little public support, right outside his front door.   I just doesn't make sense.

Mr Putin is at the moment, one of the most popular presidents ever in Russia.....he regularly polls over 60% in popularity, why on earth would he involve himself in this?

If Nemtsov had really been a danger to Putin...and most observers say that he was a decade out of date, with no power base, surely he could have been bought off or eliminated without it being done on widescreen TV?

The most likely scenario is that one of his business deals went wrong, simply a gangland hit....another possibility is anti Putin elements setting it up.