I prefer the approach of things like the TV show Leverage, where all that skill and hard work is rewarded by a plan coming together like a well-oiled machine, and the climax isn't a bunch of last-minute scrambling, it's the complications being deftly dealt with as they crop up.
Mathilde came into this knowing that someone was doing murders and they were probably going to do more, and that is a scenario that would require a lot of climactic last-minute scrambling to avert disaster. But Mathilde used the time available to learn the identity, appearance, personality, target, and timetable of her quarry, and used the Longshanks to narrow down the possibilities available to him until she could park herself on one street and be reasonably certain that at some point he'd go past.
For example, let's imagine that we
hadn't chosen to investigate Alberich's form and would not have known about the mutated arm or strange scent. (That's not to mention the fact that not having a physical description of Alberich might have made the team effort to canvas the city a lot harder and might not even have succeeded at flushing him out to begin with.)
Imagine the counter-factual scenario where we've just located this sedan;
we don't know what the identifying marks of Alberich are, which means that the players are given an update that ends with:
"You've come across a sedan that has Alberich's personal seal on it. There is an odd smell about it, and your witchsight shows the person has a sullied soul, and they're sitting weirdly. What do?"
>Attack anyway, assuming that this is Alberich.
>>Attack with the dragonflask; the body will be destroyed, but it was probably Alberich anyway, right?
>This might be a body double or servant of his. Or some other unrelated mutant entirely. Capture them and try to see if this is Alberich or might lead us to Alberich.
>Just follow them and see if they lead you to Alberich, or if they head for the Unfahigers which would tip us off.
Without a few critical pieces of knowledge, the entire situation changes because we have to act with a lot more uncertainty. Options that destroy the body become a lot less palatable. Capture or following them might become a lot more desired, because we might feel like we "can't take the chance."
That "can't take the chance of" thing shifts and flows. Sometimes it can be "can't take the chance they get away", sometimes it's "can't take the chance we lose this lead", sometimes it's "we can't be sure we can take this fight."
It would still be entirely reasonable to, in that situation, conclude that this is Alberich. "We came here looking for a sorcerer or mutant or something, and this guy has Alberich's seal on his sedan (assuming it's not a fake-out that he put on a sedan to lead people away and see if anybody takes the bait; if somebody attacks the sedan with his sigil on it, he can assume that people are looking for him specifically; if not, maybe not) so... let's go for it." But we'd probably be a bit more uncertain and concerned about things anyway.