The FBI could not account for 225 weapons, for at least a two-year period. Consider that they have about 10,000 agents, and this figure may also includes weapons missing from years past. 225 is still an excessive number, but it isn't grossly so. My experience is that any LE agency will have a about a .5% loss or theft rate per year on agency-owned weapons. A lot of that is just the normal "background hum" of crime that impacts everyone. You shouldn't leave your issued MP-5/10 in the trunk of your issued car, but you may lose a duty gun to burglars (which is I locked all my guns in the Evidence vault at work last time I went on vacation, but I digress).
Missing 225 firearms is a lot, but having done a firearms audit on an LE agency that spanned over a decade, I know that there is usually a lot more than meets the eye when it comes to "missing" weapons. Many, if not most, of the weapons that were "missing" had most likely been destroyed, but I had no affirmative records trails to prove it, so they had to go down as not accounted for. Several months after I finished my audit, I found several missing (and since reported stolen) weapons in a solvent tank in my own office. The tank was in a corner and appeared to be part of the A/C unit for the building (I have a really, really crappy "office"). I was moving boxes of crap that were being stored in my office one day (did I mention that I have a really, really crappy office?) and the lid fell off this parts washer, and I could just barely make out the outline of several old wheelguns through the muck and congealed grease. Bang, just like that I cleared up a major part of the mystery surrounding where the heck all of these weapons went. My bet is that about half of the "missing" weapons are in a chest on a range or sitting in the bottom of someone's file cabinet, forgotten. That's how it was around here, at least.
BTW, we have a lot tighter inventory controls, now.