There are gradations of wizard headband fanciness. Some of them can enhance the wearer's mind in multiple directions simultaneously, an enchantment with few cost-effective applications outside of niche spellcasting techniques and advanced statecraft. You may be wearing one of them.

… how expensive is this thing?

In a relative sense: roughly the same price as a single-attribute headband of the next tier higher. In an absolute sense: completely unaffordable on a government salary. Even if it weren't, buying one is a ludicrous waste of money if you're not a mystic theurge or a Chelish archduke.

Hmm.

Detect Magic and Identify agree: the cuirass is mundane. Gwenhwyfar spent far longer inspecting the thing than she really needed to, not only to double-check her own work but to give the detective time to acclimate to the headband.

"The armor isn't enchanted," she says, turning around, "but it's— ah, what are you doing?"

She's attempting to assert dominance by leaning forward at a steep angle, bringing her head closer to Gwen's to narrow the talking distance while still standing. This pose has the unfortunate side effect of being R-rated; her blazer's structural integrity is threatening to disintegrate like a sandcastle under high tide. It's too late to course-correct; she's committed to the bit.

"Hey, this thing's pretty snazzy! Where'd you get it from?" she asks, obnoxiously cheerful.

"Won it in a card game. What does that have to do with anything?"

"And you survived?"

"I had help. And before you ask, no, I can't sell it. I haven't found anyone who will pay me what it's worth."

"I wasn't going to— oh gods, it's horribly cursed, isn't it?"

"It's not horribly cursed. It's just Evil."

Before you go haring off with a comically inapt understanding of the situation: magical headbands do not have moral agency. You live in a world where meta-ethical cognitivism is empirically true, and Lieutenant Gwen is asserting a fact about her headband, on the order of telling you what variety of gemstones are in it.

Some headbands have moral agency! Just, not this one. This one won't start talking to you outside of your imagination.

"I'm wearing an Evil tiara? Doesn't feel very Evil. It's not going to turn me into a serial killer, is it?" she asks suspiciously.

"Not as far as I'm aware. Worst that ever happens to me is sermonizing from people who mistake its aura for mine."

The First Guard, like most armed forces that aspire to legitimacy among the ordinary people they serve and protect, is staffed with as many paladins as they can get their hot little hands on – more paladins than one might think, considering that holy warriors are uncommon and prefer to be affiliated with knightly orders, because both the armies and the knightly orders will bend over backwards to make it happen. The knightly orders do this because they are for the most part funded by taxpayers and know which side their bread is buttered on, and the armies do this because staffing certain crucial positions with paladins reduces corruption to almost nil^†, an invaluable tool in any organization. Smite Evil and Lay on Hands are also nice, sometimes.

Gwen has worked with so many paladins that no fewer than six of them have pulled her aside to deliver heartfelt warnings about the horrors of Hell. Four of them were appropriately sheepish after she removed the headband and demonstrated that she was not personally Evil; two theorized that Pharasma might frown on her use of it but were otherwise content to let her be. Gwen doesn't know how seriously to take this warning – none of the paladins in her chain of command have so much as commented on it – but the lure of mental prowess is too strong to ignore. If the headband was made with the spilled blood of innocent magical creatures (a disturbingly likely possibility) she'll put their spirits to rest herself once she's strong enough.

^†Eliminating obvious corruption is unreasonably effective at boosting operational efficiency because the art of sophisticated graft is still in its infancy. Techniques for hoodwinking paladins hard enough to get them to sign bad purchase orders are too anachronous to fit in this margin.

Your alignment is not under concern right now. If you're at risk of becoming Evil, I'll let you know.

"If I'm a lycanthrope now I'm going to bite you first," she says. "We've got mundane armor, a Gentle Repose, definitely two missing rings, probably a bunch of other missing stuff, and no positive ID. Did you get anything else off him?"

"The shoulder art is a reservoir tattoo, unless he got a nonfunctional replica. No way to tell; any working enchantment died with him. A reservoir tattoo can store a spell, third circle or lower, and hold it in stasis while you don't need it. Convenient but expensive – at least in Absalom. For all I know they're cheap in Indapatta. He would've had to pay… about as much as the headband is really worth, to get it from a local tattoo sorcerer."

She's less sure about this next part. Like most wizards, she knows just enough metallurgy to be dangerous. Probably worth mentioning anyways.

"This is just a guess, but I think the cuirass is made of mithril. It's got the right tint for it, and carbon steel probably would've buckled under the weight of the rock by now. We'd need an expert to make sure. That's all I've got so far."

That much mithril is too expensive to casually leave behind. Any number of witnesses must have tried to extract it by now, but there are no scratch marks on the metal or the rock from attempts to drag it out. It hasn't moved at all.

Mithril or not, she's prepared to believe the corpse is stuck.

"Any significance to the head trauma? Seems like it's calculated to fuck with us, unless there's a face-removal funeral rite for us to contend with."

"None that I've heard of. With the information we have so far, the face isn't going to stop us from identifying the victim. The missing jaw is more interesting. Speak with Dead only works if the corpse is capable of speech – this looks like a rudimentary attempt to block us from interrogating the victim."

"Going to the bother of de-mouthing the body means they were worried about what we'd learn. Good thing it was, ah, rudimentary? This looks fairly comprehensive to me."

"We don't need to fully reconstruct the damage, a patch job will do," Gwen says dismissively. "The rest of the body is intact enough for full answers, as long as it can produce speech. The real way to block Speak with Dead is to destroy the body, or failing that to use Speak with Dead yourself immediately after the murder. Corpses can only respond to that spell once per week."

"Oh no."

"But that doesn't even matter, because— what do you mean, 'oh no'?"