Morrowind:The Death of Ralen Hlaalo

Quick Walkthrough
# Chat with Nileno Dorvayn about business and Ralen Hlaalo.
# (Optional) Ask around town about Ralen Hlaalo, and you'll hear rumors that Nine-Toes the Argonian killed him.
# (Optional) Chat with Nine-Toes, who will deny killing Ralen Hlaalo.
# Take the key you received from Nileno Dorvayn and enter Hlaalo Manor; chat with Ralen's servant, Uryne Nirith.
# Ask around Balmora about the ''murderer's description'', and you'll be informed that Thanelen Velas meets the description.
# Kill the offender, and report back to Nileno Dorvayn to complete the quest and receive your reward.

Detailed Walkthrough
The Death of Ralen Hlaalo
Nileno Dorvayn at Balmora's Hlaalu Council Manor will ask you to find the murderer of House noble Ralen Hlaalo in town and kill him. If you ask around town, you'll be pointed to Nine-Toes the Argonian.

Confronting Nine-Toes (optional)
Nine-Toes is in his house in town and will deny any involvement in the crime.  You can choose to kill Nine-Toes and report back to Nileno Dorvayn to complete the quest, or you can choose to give him the benefit of the doubt and investigate further. If you choose to investigate further, proceed to Hlaalo Manor, just across from the Hlaalu Council Manor, and chat with Ralen's servant, Uryne Nirith. If you choose to kill Nine-Toes, just take note that he is a member of the Blades, which means that you may get expelled from the Blades, thus making it harder to finish the Main Quest.

A Conversation with Uryne Nirith (optional)
Once you locate Uryne, who's sequestered in a small bedroom on the second floor of Hlaalo Manor, chat with her and she'll inform you that she witnessed the murder. She'll then give you a description of the murderer, who she identifies as a young Dunmer with red hair, bonemold armor, and a Dwarven War Axe. With this information, you can ask around town again and you'll be pointed towards Thanelen Velas (of the Camonna Tong) in the Balmora Council Club.

Bringing a Murderer to Justice
At this point, you have a couple of options. You can kill either Velas or Nine-Toes, or both if you want to make sure. Nileno will accept either or both deaths as sufficient vengeance.

Return to Nileno in Balmora to finish the quest and receive your reward of 1,000 gold septims, and a House Hlaalu faction reputation increase of +10.

Notes
You can get this quest whether you belong to House Hlaalu or not. If you have gotten the discussion topic "Ralen Hlaalo" via other means (such as the Thieves Guild quest to steal his Vintage Brandy), you may talk to Nileno and she will still ask you to find the murderer. However, if you are not a member of House Hlaalu she will not give you the key to the manor, meaning that you will need to break in if you wish to gain access. 
Note that if you ask Nileno about Ralen Hlaalo before joining, she won't give you the key even if you ask her about Ralen Hlaalo after joining. Therefore, if you are planning on joining House Hlaalu and don't want to have to break in to Hlaalo Manor, don't ask her about Ralen Hlaalo until after you join.
It is possible to get this quest without having completed any prerequisites. Simply break into the Manor and talk with Ralen Hlaalo's servant, who will give you the murderer's description when asked about the "murderer's description" topic.
Thanelen Velas is one of the targets for Larrius Varro's quest, so you can complete both of these quests. Nileno will still pay you the thousand gold reward and may ask you to join House Hlaalu at that point if you are not a member. This quest will be instantaneously completed, if you have already killed Velas.
If you kill Nine-Toes you will complete the quest and not get a bounty on your head. In order to kill Thanelen Velas without receiving a murder bounty, you will need to provoke him into a fight.
Hlaalo Manor makes a pretty good free house at the beginning of the game. Large and centrally located with plenty of storage space, the only occupant is Uryne Nirith, and she never leaves her room. As a quest item, Hlaalo's body never goes away, and basically amounts to a container with infinite capacity, although you can use the console command 'disable' to remove it.

Bugs
 
 

Quest Stages