Question --- Why Communication with the Dead is Not a Good Idea
From The World and Everything In It
Several reasons why folks don't communicate with dead bodies in order to question them about the past come to mind. First, and I suppose most obvious, is, well, they're dead. The dead tell no tales. Strictly speaking not entirely true, but for the most part, dead bodies are a pretty quiet segment of the population.
Now, it is possible for a sufficiently powerful & dwimcrafty wizard to reanimate a corpse. This is the subtil and delicate art of Thanetometry. Depending on the quality of the corpse in question, the result might be a skelleton warrior or a witless zombie. These are, of course, absolutely useless for just about anything except lurching in hordes seeking to KILL KILL KILL!!!!!! Relatively simple ensorcelments control their activities and no original thought arises from within.
Only a very fresh corpse can be used for anything that requires some basic thought on the zombie's part. You might, in some quarters, find a very posh gent whose butler reminds one very much of his grandfather's butler. And this would be because old Swithins was, in point of fact, the grandfather's butler, only when he died he was made into a zombie. On account of him being quite fresh at the time of processing, his mental faculties as a zombie are relatively intact. He knows the house, where everything is, what needs doing. So long as things remain the same, and in posh houses, they generally do, he could remain an efficient servant for centuries.
Now this is a very expensive proposition, on account of the deep and extensive magics that have to be engaged in. A skeleton warrior is a relatively simple and cost effective reanimation charm. A skilled wizard working quickly can put together a reasonably large force within a month, at perhaps half a dozen per day. Dear old Swithins would have required considerable anatomical & physiological knowledge on the part of the wizard. He'd have to have some understanding of how a body works in order to get and keep a dead body operational. Without too many bits falling off.
Getting such a thing to not only talk but recall and converse is very high magic indeed. The most successful such thing was the now legendary Skull of Skanderdag. Skanderdag was, as everyone knows, a young blacksmith who made himself into a great warrior and hero in some age past. A regular conqueror of warlords and beautiful women alike. Though the warlords rarely survived long enough to appreciate Skanderdag's prowess with his long straight sword.
Now one of his chief rivals in the warlording game was a fellow by the name of Skoombug, and Skanderdag had his head turned into a divinatory device after he was slain. Using Skoombug's knowledge, Skanderdag was able to defeat Sithur, a really big-time warlord (and who, incidentally, had slain Skanderdag's family years before).
As you might suspect by now, while Skoombug knew a lot about the warlords of his own day, as time went on his knowledge began to fail. Skanderdag, now quite reliant on his skull of divination, began to lose his territories and was eventually himself overthrown by a strapping young lad with his own long sword, itching for adventure.
And so passed the legendary Skanderdag.
It would be quite possible to recreate the same ensorcelments and use them on, say, a murder victim. A murder victim is, of course, the single best witness to the crime in question. But there are several problems that prevent thanetometrists from being called in on murder investigations. First and foremost is that murder victims are rarely discovered and zombified within an hour or so of death.
The mind and awareness of a person, quite apart from the person's soul & spirit which have already departed, are quite the ephemeral parts of one's being. As the brain dies and its structures begin to fail and its physical part begin to decompose, it becomes rapidly more difficult to secure the person's remaining mortal mind and awareness in anything like a usable state. Memories become tatters, ideas become dissociated, images become shattered and by the time a couple days have passed, nothing at all will remain that is in any way useful.
I can't imagine the City Guard would waste any resources on an ordinary urchin found murdered in the street. They might try if a sufficiently, mm, valuable member of Society was found attacked and near death and a powerful thanetometer could be found and made to prepare in advance of the victim's imminent death.
In theory --- quite possible. In practice --- not at all practical. There are also, of course, ethical sequellae to follow such treatment. Take a look back at old Swithins. When he was zombified, it was most likely done with his consent, and at great expense and he does need to be looked after. You know, routine maintenance. But he's got a stable, wealthy, upper class family to look after those needs.
If the government decides that a murder victim is to be judicially zombified, that places a great burden in time and treasure on the victim's family. Especially if they have limited means. I mean, what do you do with your daughter, now she's a zombie? I mean, I guess you can hire her out as a washer-girl or something. What do you do with her when you die? Who's going to continue looking after her? She might end up being auctioned off along with the rest of the furnishings. Or perhaps some worse fate.