[DAO Spoilers] The Death of Arl Urien and Oriana
Bodahn said the Arl of Denerim was killed before he ever reached Ostagar. It is unlikely such a powerful noble could be killed by bandits, so it must be assassins.
It is rumored his son, Vaughan, was the culpit, who hired crows. However city elf origin prelude should disprove this theory. Because he said to elves "My father would do this or that", he didn't say "I would do this or that." That implies he expected his father to return safely. He didn't need to lie to those elves, or give them a false impression, for he regarded them as nobody. Vaughan wouldn't bother to lie to them.
So either Loghain or Howe hired assassins. They both have motivations. The problem is, Howe led his army to Denerim before Loghain returns (otherwise it would be Loghain, not Howe, cracked down elven riot). So how could he know Urien wouldn't come back to settle score with him? Either he sent assassins himself, and knew Cailan, Loghain or other nobles, especially those loyal or friendly to House Kendells, wouldn't or couldn't punish him for it, or Loghain sent them and Howe knew it beforehand (thus he knew Urien wouldn't return).
Now let's see Oriana's case. Howe may have reasons to kill other Couslands, but killing Oriana is outright stupid. Without her, Fergus is now free to marry again, thus gain the freedom to use his new marriage to secure new alliance with other Fereldan nobles, to obtain additional soldiers and money to support his effort to reclaim Highever. If Howe captured Oriana instead of killing her, that would make Fergus' situation awkward. Either he abandoned his wife, now a helpless captive imprisoned by his enemy, that would seriously damage his reputaion, or he must lose the chance to build new alliance by another marriage. Howe's action only makes sense if he knew Fergus, like Urien, wouldn't survive.
And I notice Howe didn't defeat, let alone destroy Highever or Denerim's army. His enemies' real strengh in a civil war, at least in short term, are not castles or cities, it's their armies. It lies on those professional soldiers, knights and men-at-arms who couldn't be replaced in any time soon. His victories are then incomplete, flawed. However, somehow he knew ahead those two armies, potentially more powerful than his, wouldn't pose a threat.
Any careful analyse must point to the same conclusion: Loghain and Howe planned everything beforehand, to remove (most powerful) potential challenges from Redcliffe, Highever and Denerim in a single strike. It's a coup of massive scale, nationwide. It's an inevitable result of polarization of Fereldan politic during the reign of Cailan.
Well, just some my idle thoughts after reading all those "Loghain isn't evil", "Loghain doesn't work with Howe", "Loghain is innocent". Bah, he is as innocent as my little finger is King of Ferelden.