I would not recommend saying this in a real life situation, even if you are robbed. It could quickly turn into a "mob justice" situation much worse than the theft itself.
More racist sentences? Why so many references to stealing in the Swahili? Is D.L trying to say that Africa is full of thieves? How about the U.S., France, U.K etc.?
Why are you inferring that this refers to an African person???
Why can't i say "huyo ni mwizi?"