Iorveth says, "Elyas must've known I learned of his madness, he fled the city." implying he compared the shard with the blade and they matched.

I have failed this mission, since after I have found the body and arranged the Succubus meeting with Dandy, I followed the main quest till noon ( Peasant were to murder the prince). I must replay it another time, really:P Sounds interesting.

yeah it totally makes sense to reserve this quest for later and go on the main path since Triss is kinda important buy you end up not finishing it. Poor design I say, they could fix it by making Elyas stay after Iorveth leaves it'd still make sense.

Elyas leaves, really? That's so strange since the rest of the Scoia'tael stay. Way to break a quest, lol.

Wait what?:-O

Are you guys so geeky that you always believe anything the girl says eventhough she's
i) electronic
ii) a demon
?

It's a well designed quest but I suggest you try the other path, too. It's not like the succubus will deny anything, claim she was framed etc. Go figure.

I always try all 'paths'. This quest is up to the player, really, there are enough 'evidences' that either of them could have done it. Although Elyas fleeing the city and confronting you points to his guilt.

As for the majority siding with the succubus, well, the case against Ele'yas (and he doesn't even know for sure you have any evidence, since you spoke only to Iorveth after visiting the crypt) is strong enough to make him flee and later attack you on sight; talk about guilty knowledge... Unfortunately, there is not the possibility to explore the hypothesis that Ele'yas himself was being framed.

You're right that it's a well-done quest and should be played both ways for full effect. It's a recurring dilemma for our Witcher: in his world, some monsters are sentient, and their crimes may be exaggerated or imaginary, or they may be victims of human fear and hatred or even a frame-up. There is often a reasonable case that the monster is innocent or should be saved, when Geralt is called upon to play judge, jury, and maybe executioner. That's what makes this game special. There is no certain truth, only lesser evil.