The biggest danger is that it may be effective
I used to live in one of those postcode areas where "If it wasn't nailed down it was immediately nicked and if it was nailed down then it just took a few minutes to pry it up". Most people in that area were ordinary people, more or less, with only a relative minority being the actual criminals. After a bit you even got to know who was the likely puerp, the cops knew it as well but there's a lot of distance between knowing who the villain was and catching them with enough evidence to nail them.
The algorithms just systematize the informal data collection and area knowledge of the beat copper of old. They should be more objective than an individual and so a lot more effective. The algorithm may seem to be biased, especially when its first used, because it has only existing data to work on, data that is probably biased. It will rapidly adapt, though, and you'll quite likely to find that its stopped being interested in dark skinned people in wool hats and started zeroing in on ostensibly respectable people who almost seem to fit in but don't quite.
I should remark that as an ex-inner city dweller I'm not particularly 'pro' police. They're only human so they can spend far too much time going after the low hanging fruit (i.e. bothering me and my friends). I never found them particularly biased against creed or color but they do get a bit cynical about offenders since that's their stock in trade. This is what tends to cause bias -- they see the same faces, the same sorts of people day in, day out, so they tend to make generalizations about people. The computer may go a long way to putting them right.