Say Magus A murders Magus B by conjuring a sword CrTe Diameter duration, with enough Penetration to get through Parma Magica of Magus B. Stab in the back with no witnesses.
Inquisitor C later examines body of Magus B.
Can they tell if it was a magical attack?
The primary rules and guidelines around detecting spell traces and the sigils that they hold is in HoH:True Lineages in the Guernicus chapter along with some other investigative spells in common use by Quaesitors.
[edit to actually answer your question:] it isn’t explicitly stated as far as I know whether a spell trace is left by a conjured item on the murdered person but the room or area where the conjured thing was conjured initially would definitely have a spell trace left there that would be detectable by those trace-perceiving spells.
Interesting. Will have to dig up that book later.
Say Magus A does some acceptable conjuring before witnesses, then conjures the sword/dagger unseen, before heading off to off Magus B.
Could Quaesitore C ascertain thar the murder weapon was conjured there? CrTe 10 from memory, and if the other conjurations were of higher magnitude...?
Far as I understand the rules without checking, every spell trace is visible since those spells are usually cast as magical sense spells. Though low level (and lower duration) ones degrade and then disappear faster but even a first Magnitude spell takes months to fully degrade to whatever negative value makes it undetectable. In that same section, I believe, are PeVi spells to degrade the traces prematurely… but casting those spells also leaves traces so what you really want is the spell mastery that lets you mask your sigil which a Quaesitor may be able to tell has been used if they have the right spell mastery for their Trace detection spell but far as I know there is no actual method to discern the real sigil if that mastery has been used.
Yes - an experienced Quaesitor could. See HoH:TL p.71 Acute Sense, p.71f Spell Traces and Signs, p.72 The Discerning Eye and p.75 Sight of the Sigil.
Simply covering a spell's minute traces with traces of a stronger spell in the same place will not fool the Quaesitorial investigator, and neither will simple Imaginem magics.
This would become a battle of acumen: research and preparation of the would-be assassin against experience and specialized magic of the Quaesitor.
Also, the power of some of the magic of Quaesitores (especially p.71 Acute Sense and p.76f Fenicil's Rituals) may not even be known to the larger Order. So the would-be assassin might not really know what he is up against.
On the other hand 'magus A conjured a 4 pound steel object here" is hardly a smoking gun- quaesitors do need to actually investigate, they can't solve a mystery just by casting spell (unless the perpetrator is really inept)
The real question is why they didn't use a real sword / dagger so that Parma is irrelevant, then destroy it with Perdo.
Perhaps the spell sigil of Magus A is such that there would be obvious traces after a Perdo spell?
But I may have written myself into a corner. Unless examining the wound indicates it was made by a 6 foot long Zweihander, that nobody brought to the Hermetic Fair. except for the bodyguard of Magus D.
Take a leaf out of Christie. You don't solve murders by forensics; you solve them by motive, and the inexplicable action which doesn't fit.
It should suffice to invite magus A at the next Tribunal meeting to testify.
Endorsing Testimony (HoH:TL p.64ff) will be offered by the Quaesitores.
He can decline, but unless he has an - ahem - very special following, the Tribunal will condemn him then for offing magus B.
Useful thoughts, that I hadn't thought of. Perhaps the Magus hadn't either. (Though with his INT stat?)
Still playing with this idea of magus murder at the Hermetic Fair.
Rather than CrTe a whole new weapon, what about MuTe a replica of somebody else's weapon?
Perhaps there is a demonstration of martial abilities of some of mage's grogs/Companion. Weapons get chipped. If Magus A gets ahold of metal chip from somebody else's weapon, could he use the chip as an Arcane Connection to the original weapon to effectively clone it via MuTe? Then stab Magus B, hide the cloned sword until it reverts back to a metal chip, that can easily be disposed of (say, toss in the blacksmith's fire)
The downside to MuTe Arcane Connection means it is a much higher level spell, so Penetration will be ... poorer.
Maybe Magus A won't get the physical satisfaction of stabbing Magus B and leaving evidence implicating his enemy.
Corrupting / blackmailing the investigating Quaesitor? There are some Tribunals - including the Rhine Tribunal - who have only very few Quaesitores.
You could always just use a non-magical weapon so you don't have to worry about MR.
There are several magical ways you could gain/dispose or hide it.
ReTe teleport spells with an AC fixed to the weapon and your lab would allow you to leave it in your lab until shortly before needing it then you teleport it to you, stab the other guy, and teleport it back. You can work with a shorter distance (such as 500 paces) if you use a chest with your baggage instead of your lab.
Enchant a pouch to shrink metal objects put into it to 1/10,000 their volume (it would need Group, Concentration, maintains Concentration, and unlimited uses a day). Fill it up with coins and other such items along with the weapon. Make sure you use it all over the place including where the murder is going to happen so its sigil will not stand out.
You can do lots of things in that vein. An additional thing is to coat the blade with a poison of the Form your target is weakest against. Just don't try stabbing a Terram specialist with a metal weapon.