Government Hired Them:
Government got tired of dealing with rioters by openly firing guns at them, pummelling them with truncheons and smothering them with tear gas. They decided to try whipping them incognito. So they created a special secret whip unit.
This is the weakest theory, because if Kale Kayihura wants you whipped, he does not need to disguise himself. All he needs to do is wait. You are going to step out of line sooner or later.

Traders formed a vigilante squad:
Because they got tired of this bullshit — who wouldn’t?– and decided to take matters into their own hands. Besides, the police were not doing enough to protect their property. Police’s concern is dispersing the crowds, not keeping crowds away from the various telephones, DVDs and items of lingerie on display in the shops, and a lot of you actually try to make sure you are dispersed TOWARDS the lootable merchandise. You need canes.

Besigye Did It:
Besigye is the only reason Museveni still gets enough votes to win an election. If we remove Museveni we will have this fuming, conceited, belligerent, tantrum-throwing, blinded-by-fury, tunnel-visioned, rageaholic hard-on sitting in office with the actual legal powers to enforce his rage. Don’t get me wrong, I want change as much as the next guy, but unless Warren gets saved before the next elections, I am voting Sevo again.
Anyway, the theory is that he is the one who formed the squad. He told them to make sure WBS cameras catch them running around the Central Police so that he can have something new to complain about.

Former Lumumbists, Former students of Namilyango College:
Because that is the sort of thing they do. Just grab a special to town, pick up sticks and start lashing at people, lashing at people. The riot was a coincidence.