The Outer Worlds: Spacer's Choice Edition

The achievement unlocks when you investigate all four suspects and report to Ludovico. The dialog choices regarding each suspect do not matter. The achievement pops when you complete the dialog pertaining to the 4th & final suspect. The sequence of the four investigations does not matter. However, the achievement is missable.

When talking to Ludovico before reporting on the 4th suspect, do NOT select the option, I know who killed Halcyon Helen. If you do, the story segues into the end game and this achievement is no longer available. In other words, do NOT start An Unfinished Accusation until you unlock the Interrogo Totus achievement.

An Unfinished Accusation begins when you talk to Ludovico and choose the option, ”I know who killed Halcyon Helen.” This advances the story towards the end game, but you lock yourself out of the achievement if you do so before completing all 4 investigations. For that reason, make sure you investigate the following suspects by completing their associated quests—the specific order of quest completion does not matter:

• ➤ Bertie: Prince of Tossball
• ➤ Spencer Woolrich: The Man Who Chafed
• ➤ The Prophet: The Productivity Queen
• ➤ Sedrick: Lord of Blight

When you report to Ludovico regarding the 4th and final suspect whoever he or she might be in your playthrough and conclude the ensuing conversation, the achievement pops. In each report to Ludovico, some of the dialog choices lean towards the suspect’s innocence others to the suspect’s guilt. Nevertheless, dialog choices regarding the suspect do not matter. Select the ones you prefer.
The above video demonstrates a playthrough where Sedrick is the 4th and final suspect. After reporting to Ludovico and concluding the dialog, the achievement pops. Note that, in the video, when reporting to Ludovico, one of the choices is ”I know who killed Halcyon Helen.” Selecting this option before reporting on Sedrick would have voided the achievement and made it missable. Had this occurred, the remedy would have been to load a save or auto-save created before telling Ludovico you know who killed Helen.