[Karl-Johan Norén, Pam Korda]
In [LOC: 46, Beyond the Gate, 580-581], Demira Eriff of the Brown Ajah, a member of the Salidar Embassy, is attacked by a group of men dressed like Aiel. The attack occurs after she's been followed from her inn by the same group of "Aiel." She was going to meet an informant from the Caemlyn Palace, who does not show up at the appointed meeting place. Demira concludes that her informant had not received her message. As she turns to leave, a man on the street leers at her, and she ducks into an alley. The particular alley she goes into is deserted. A bit further along the alley, she runs into the men dressed as Aiel, who stab her with spears. She is severely injured, but not killed.
In [LOC: 46, Beyond the Gate, 584-586], we learn more about the attack. Right before Demira was attacked, a man came into the inn where the Salidar Embassy was known to be quartered, and "said he had seen Aiel following an Aes Sedai-- he described [Demira] exactly-- and saying they were going to kill her." Demira's Warder ran with another AS to save Demira. Demira remembers that one of her attackers told her, "Tell the other witches to stay away from the Dragon Reborn." This message, along with the fellow at the inn, and the fact that Demira's wounds missed vital organs indicate that Demira was meant to survive, and that the attackers wanted the Salidar AS to believe that Aiel were behind the attack.
We don't know for sure who ordered the attack, but we can almost be sure that the attackers were not real Aiel. For one thing, one of the attackers is "a squat fellow with villainous eyes." From all descriptions, Aiel (especially the warriors) are tall and lean, certainly not "squat." Secondly, the Aiel do not refer to the AS as "witches," nor do they refer to Rand as "the Dragon Reborn"-- that is a wetlander prophecy. Thirdly, one of her attackers is described as having "mocking black eyes". Aiel do not have black eyes [Sheryl Smith]. Aviendha mentions this specifically: "'I never saw black eyes except on a peddler until I crossed the Dragonwall'" [WH: 27, To Surprise Queens and Kings, 522].
What was the motive for the attack? We can get ideas about this from the wide-ranging results: the Salidar Aes Sedai believe that Rand arranged the attack, and retaliate. The retaliation drives Rand into leaving Caemlyn for Cairhien, and sets his mind against the group of Aes Sedai most likely to help him. He turns towards the Tower Aes Sedai, who trick him, capture him, and abscond with him locked up in a box, to be rescued by Perrin, the Aiel, and Taim. The overall result is a great deal of ill-will and distrust between Rand and the SAS, Rand and the TAS, and the AS and the Aiel. It is reasonable to conclude that all or part of this was the motive for the attack. Fomenting discord among Rand's possible allies seems to be a general goal of the Shadow's agents, so any of the Forsaken could have had a motive for setting up the attack. The Tower Aes Sedai could have organized it, in order to drive Rand away from their Salidar rivals. Taim has made efforts to turn Rand against the AS on many occasions. He could have done it on his own initiative, or perhaps Demandred arranged the attack through Taim in order to drive Rand away from the SAS, and make him vulnerable to the TAS (whose kidnapping of Rand was likely instigated by Mesaana [LOC: Prologue, The First Message, 58]). This theory is attractive because Demandred and Mesaana were working together (with Semirhage, how does she fit in to this theory?) in LOC on a plan to "let the Lord of Chaos rule." That was, after all, the final result of the events triggered by the attack on Demira - chaos definitely ruled at Dumai's Wells.
First, it was a very well organized and planned attack. It is done after Demira is shadowed and possibly lured (or even Compelled) into small, empty alleys. The attack is done by people meeting her. Simultaneously, a man appears bringing the message to her Warder at the Crown and Roses. The interception may mean that other people directed the "Aiel" to their position and cleared the alleys, giving 10-20 people participating, of which at least a few must know Caemlyn very well or that some channeler was part of the group. Furthermore, the attackers must have intercepted the message to Demira's informant.
There's reason to believe that Compulsion was used:
"Turning away from the gate, her [Demira's] eyes chanced to meet those of a tall, lean-faced fellow in a carter's vest who was gazing at her much too admiringly. When their eyes met, he winked! She was not going to put with that all the way back to the inn.... She slipped into the narrow shaded gap between a cutler's shop and a tavern."
It seems like too much of a coincidence that just because some fellow leered at her, Demira chose to travel back to her inn through a deserted alley - the particular alley where the "Aiel" were waiting in ambush. The point that the ambushing team used channelers is strengthened by the fact that Demira couldn't reach saidar:
"Frantically she reached for saidar, but something else pierced her side, and she was down in the dust. That remembered face was thrust into hers, black eyes mocking, growling something she ignored while she tried to reach saidar, tried to... Darkness closed in."
Granted, she was injured, but Moghedien was able to channel with an arrow through her chest, Rahvin while being BBQ-ed and Nynaeve while about to lose consciousness from asphyxiation.
Now, it is not certain that channeling was used in the attack, either to force Demira down the alley or shield her. However, the extremely close timing involved (the message to Demira's Warder came right before she was stabbed) indicated that she did not go down that alleyway by coincidence. The leering fellow may have had a backup plan for getting her down the alley if his antics didn't work - it just turned out that they did. As for shielding, John Hamby points out that Demira doesn't feel that she's blocked from the Source, just that she's having trouble embracing the Source as two spears are driven into her. Yes, Moggy could do it with an arrow; but Moggy is stronger and more skilled, and Nynaeve is Wonder Woman.
The attack is done after the embassy had met Rand three times, with no meeting on the day of the attack. This means that the attackers had either a maximum of three days of preparation or knew about the embassy before it met with Rand.
So we have the following requirements for the group who did the deed:
By far the best candidate is Taim, either as "plain" Taim or as Minion Taim. The Asha'man fulfill every demand above, and Taim also has the political motive and chutzpah to do it. It would be strange if the Asha'man did not include people from Caemlyn (since they are based near that city), and they are being trained in the use of weapons, and they include some men who are already acquainted with weapons. Taim also knows of the embassy early because Rand tells him of it. He likely hates Aes Sedai, and is clearly interested in bringing Rand closer to him and away from all things AS. It's not much of a stretch imagining the Asha'man referring to the AS as witches either. In fact, a few days before the attack, Taim suggested arranging "accidents" for the Aes Sedai in Caemlyn [LOC: 42, The Black Tower, 545].
Apart from Taim, the other major suspects are the Tower Aes Sedai, the Whitecloaks, Padan Fain, and Joe Random Forsaken (i.e. not Mesaana or Demandred).
The White Tower AS (acting without influence from Mesaana) can be ruled out, because they would be hard pressed to simply reach a decision so fast. Pigeon to Elaida, Elaida decides, pigeon back, plan and do attack. Done in three days? No way. Also, the White Tower lacks people and organization in Caemlyn.
The Whitecloaks can also be ruled out. They have withdrawn their organization from Caemlyn, and their lower ranks would be more interested in killing AS than in subtle political maneuvering. Niall might try something like this, but the Niall POV scenes we get in LOC and ACOS show him concentrating on schemes involving Morgase, the fake Dragonsworn in Altara, and later, the situation in Tarabon - nothing involving Rand and his connections with the Tower.
Fain could have some motive to drive Rand towards dealing with the Mashadar-tainted Tower instead of the untainted Salidar AS. He does have access to DFs from Caemlyn, and the former Whitecloaks. But, as he thinks when he is reached by the report of the Gray Man attack on Rand, his resources are rather limited. He doesn't seem to have access to the number of followers required to pull off the attack. Furthermore, everything we've seen of Fain thus far has had him ingratiating himself to one powerful person, and corrupting them. The attack on Demira doesn't fit his style - it's too indirect.
An attack from Joe Random Forsaken is the most likely, next to Taim. As stated above, the Shadow seems to have a general strategy of creating discord between Rand and his possible allies. Furthermore, as Bob Kluttz points out, Demira was interested in learning about the Seals on the DO's prison [LOC: 46, Beyond the Gate, 580-581]. A couple of weeks after the attack on Demira, Herid Fel is spectacularly killed for his interest in them, and later in COT, Bashere's wife and Dobraine are assaulted on the mere suspicion that they were guarding one or more of the seals [COT: Prologue, Glimmers of the Pattern, 70 & 93]. The fate of the seals is somehow critical to the Dark One's success. If this was the main motive for the attack, Demira wouldn't have been left alive. However, it could have been an additional motive for choosing Demira as a target, rather than one of the other SAS. This idea pretty much requires whichever Forsaken planned the attack to have had a strong power base in Caemlyn. The only Forsaken of which we know this to have been true is Rahvin, and he was dead by the time the Salidar embassy arrived. However, this doesn't rule out somebody having resources we don't know about.