I havent worked out motive quite yet, but...

Lord Elegar and Alteima are the two servants (either that, or the female servant is the young red sister that Rahvin captured in the prologue)

The two servants previously mentioned both have physical characteristics in common with Lord Elegar (the male servant) and Alteima/Unnamed Red (the female servant) i.e

Unnamed Red: "Lounging in a gilded chair in his shirtsleeves... etc and so forth...There was a slight glaze in her large, brown eyes" (TFoH, Pro)

Lord Elegar: "That done, he released Elegar's mind as well. Lord Elegar. A minor noble, but faithful to his vows. He licked his thin lips nervously" (TFoH, Pro)

"The woman's brown eyes rolled up in her head, she would have collapsed in a heap if the man had not caught her, and, his narrow mouth was working rapidly, as if he were praying, but could not get the words out"

On to means (with a smattering of opportunity)

these guys, whether elegar and alteima, or elegar and a Compelled red could have been hiding behind this small door, which could easily be a broom closet outside of the queen's apartments (I believe the room next to the courtyard is the queen's sitting room, as evidenced by chapter 19)

Asmodean, walks through the sitting room, down the corridor, sees a door, opens it, thinking it's a pantry (my pantry is roughly the size of a broom closet at home, is yours?), and elegar and whomever stab him to death and drag him inside

Why were they hiding?

Elegar and Whomever were hiding because they were in collusion with Rahvin in one shape or form (darkfriend and dupe, perhaps), and were scared of rand

Why did they kill asmodean?

Simple... if they'd told him "there's no beer in here... try down the hall" and closed the door, he might have been suspicious as to why people were hiding in a broom closet

Why did asmodean say "you? no!" before they killed him?

When you're walking down the hall in someone's house looking for a bathroom, and you open the wrong door, and you see someone you met at a party 3 years ago, you're going to say "you?" or "what the hell are you doing here?" to that person... and when they stick a dagger in your chest, you're going to say "No!" too

how did asmodean recognize them?

Or maybe, asmodean recognized him/them... Elegar is a known darkfriend... Asmodean has probably communicated to him in a dream or something, or met him at the darkfriend christmas party

Here are two step by step theories of what I think may have happened

1) rand freezes the myrrdraal and guardsmen, sees elegar and unknown girl, he stammers his apologies for getting blood on the carpets, and saunters off

elegar recognizes the dragons and is beside himself in terror, grabs the girl and hides in the broom closet

(there are no palace servants to redo the linens, so this is a good a place as any to hide)

rand kills rahvin, etc and so forth

asmodean wants to get hammered, walks down the hall, sees the door, opens it

elegar et al sees they are about to be discovered and kills him

elegar drags body in and recognizes asmodean, he says "oh (crap)" and they high-tail it out of there and hide his body in a cement post or the equivalent

this is bourne out by the fact that when elegar sees taim in the first chapter of LoC, he throws up (you would too if you had just come face to face with another forsaken who may or may not know that you accidentally killed his comrade)

2) rand freezes the myrrdraal and guardsmen, sees elegar and unknown girl, he stammers his apologies for getting blood on the carpets, and saunters off

elegar recognizes the dragons and is beside himself in terror, grabs the girl and hides in the broom closet

(there are no palace servants to redo the linens, so this is a good a place as any to hide)

rand kills rahvin, etc and so forth

asmodean wants to get hammered, walks down the hall, sees the door, opens it

elegar knows from rahvin that asmodean is a traitor, and puts a daggar in his chest

3 reasons why these theories dont make sense

1) there is no evidence that Elegar et al have ever met asmodean or know what he looks like

2) why doesnt rand recognize Alteima (whom he exiled) or Elegar the next day when he meets him

3) this theory isnt convoluted enough to fit jordan's writing style; WoTists opperate on a form of reverse occam's razor, if the explanation is simple enough, it probably isnt true

2 reasons why these theories make sense

1) no one has claimed responsibility in PoV... that is, no one:

Graendal, Sammael, Demandred, Semirhage and Moghedien all either seem surprised, or wonder what happened to him

What other PoV character known up to this point (who isnt seemingly dead) has a reason to kill him?

2) the means of death is attributed to the power almost exclusively, but nowhere does it indicated the power was the weapon... the Dark One never said Asmodean was balefired, only that he was a traitor... he did say rahvin was balefired, and I count that a significant point... the dark one only said that asmodean was a traitor and that he was twisted by his weakness (which could mean that the dark one was watching, knew that asmodean was looking for a drinky drinky, and happened into someone who didnt want to be discovered, though I think that unlikely), the book says that "Death rook him"... that could mean anything... Death in some personification would have bundled him into a carriage, he could have been balefired, or he could have been so startled he knocked over a hoe (he was near a garden), it fell and cracked his skull, or he could have been stabbed or had his head chopped off... logically, we must assume a human cause... someone butchered him with the Power or with a weapon... but it could have been either, so the killer neednt be a channeler (I will note that Alteima is noted as someone very good with poisons... poisons exist which kill in less that a second)

I actually have an alternate theory which is really silly

Asmodean's killer may have been the man he found dangling from a cliff holding a tuft of grass... he may have survived the plunge, and been waiting to take his revenge the entire time

Wouldnt that be poetic justice?

"It was not that he had been reborn a new man at all, but he would cling to that tuft of grass on the cliff's bank as long as he could, the roots would give way eventually, the long fall would come, but until then he was still alive.

He pulled open a small door, intending to find his way to the pantry. There should be some decent wine. One step, and he stopped, the blood draining from his face.

'You? (I saw you fall, I knew you were dead) No! (Dont kill me... I was going to help you, I just forgot!)" The word still hung in the air when death took him"

If y'all could get back to me, either to praise my perspicacity, or to say I'm a dolt, that would be nice =]