Yes, but I think the main goal of these early trials is not getting the thief caught by the robot at this time, but watching what problems arise, seeing what works and what doesn't in the interaction of the robot with the people who is supposed to be there, learning from its errors, getting to work out better algorithms for patroling (so they are not so easily fooled like the military bots in Deus Ex, for example), so they have this information available when the time comes for designing the next one. After all, it took six generations to get Roy.
So, saying that it has no purpose is not true, I think. It is unlikely that they'd invest lots of money in things with no purpose.
An additional thought. Considering the recent love affair of police forces with tasers (particularly in the U.S. ... good God, they tase everything that moves nowadays, from 8 year old kids to 75 y.o. grannies), they might put a taser on these robots so they are "not lethal" but can start practicing human targets interception, something we know
will be a highly "desirable" feature in robots over the next decades.