It does seem extraordinary. An hour and a half after the first stabbing and he was still walking and attacking.
Unless you can absolutely flood the entire area with enough police to ensure no can can move from one street to another, then no it's probably not surprising that in a reasonably large town or city the hunt for someone can take hours, as unless you've got them in sight all the time you have to start the search anew every time you lose them, and in most towns and cities within a few minutes you can be well and truly lost to the police (a helifcopter can help if you can get it tracking the person, otherwise it's just going to see people).
Given there are a very finite number of officers able to respond within a given timeframe, and the guy was moving around, whilst the officers would initially have been concentrating on his last known attack (with officers getting information and protecting paramedics), by the second or third attack there may have been no more officers able to get there for several minutes, and by that time he could have been several streets away even if just walking.
