The First Murderer
Locations: Nexus, Eos.
This one kicks off in the Militia Office of the Nexus. Talk to Mariette, the green faced turian by the desk, who greets you with a song lyric.
In classic sidequest form, she relates that her husband has been jailed for a crime he didn't commit. Investigate further by crossing the hall to the Operations detention center, and talking to Sergeant Aker.
He'll give you leave to interrogate Rensus, who tells you his story.
Then, it's back to the Militia Office for a chat with Kandros, who will grant permission for further investigation.
He gives you two leads, but one is right behind you, a pillar-console with an audio recording of the confrontation.
The other is back up in Colonial affairs, crewman & witness Cassidy Shaw.
Exhaust her dialogue options to discover that the victim's body was never examined, and Tann vetoed retrieval. Follow up with Tann
He'll give you permission and coordinates to follow up on the killing (though forensics on a corpse abandoned weeks ago, on a battlefield, in a duststorm may be tricky). On Eos, follow the quest marker to a spot east of the lake and due south of of the Promise outpost.
Scan Reynold's armor to learn that the man himself has been torn apart by the local wildlife. Continue to follow the markers, each one a fragment of the Chief's armor that points the way to the next.
The trail ends in a Kaerkyn hive- use the Nomad's tires to thin resistance, then take out any stragglers the old fashioned way.
Snag the minerals by the cave entrance if you haven't already, then venture slightly inside the cave for the last cache.
This will reveal that Reynolds was felled by a Kett weapon- but Rensus did fire at him fully intending to kill. Hmm. Back on Nexus, you can confront Rensus with the evidence. He feels that since his shot missed he's innocent, because apparently there is no law against attempted murder in the Alliance.
No matter what your response here, you'll end up taking the matter with Tann, who will toss the decision right back to you.
This is toughie, because neither choice is quite correct (attempted murder really is a crime), but it's probably better for the station as whole to show mercy here. It resets the murder count to zero, and dispels the idea of a solider killing his commanding officer. Whichever way you decide, drop by the jail cell afterward to see the immediate consequences.
If you do free Rensus ,you can catch up with later in the Hyperion Cryo Bay, where he intends to slink back into deep freeze until this whole thing blows over.