Investigate the Murders Walkthrough in Baldur's Gate 3

Enter the Monk Temple in Rivington and speak with Valeria and another NPC (non-player character — anyone the game controls, not you) to start the Open Hand Temple Murder quest.

The NPC will direct you to Sharess Caress. Speak to the attendant at the counter, then go upstairs to speak with Valeria.

Go to Fraygo's Flophouse, head upstairs, and use a ladder to reach a loft. Smash a bookcase to reveal a secret bedroom.

Pick the lock on the bedroom door to find a bloodstained note with names of murder victims and a bloodstained bed. Interacting with the bed allows for checks to find the missing brothel worker.

Return to Sharess Caress and inform the attendant of your findings. Show Valeria your evidence to update the Investigate the Murders questline. Valeria will give you a key and a letter to access the Lower City.

Once in the Lower City, follow the quest markers to the locations of the NPCs on the murderer's list.

To protect the NPCs, find Filago at a clothing store near the road to the Baldur’s Gate upper city waypoint (a marker on your map you've manually placed as a destination), beyond the wall near Sorcerer’s Sundries.

Enter the store, defeat the murderous dwarf and his shapeshifter band, and take the hands in the pouch as evidence. Read the note on the dwarf's body.

Locate the Bhaal temple beneath the Candulhallows’ Tombstones building, north of the Elf Tavern.

Inside, find a painting at the back of the building and activate the hidden button behind it to reveal a secret door leading to the Crypt.

Approach the guards inside the Crypt and use the secret phrase found on Dolor's body or show the bag of hands as proof of the murders.

Speak to the speaker of the cult to learn about Orin and her Bhaal followers. You can find Valeria chained up; you can choose to free her and fight the cultists or refuse to blow your cover (press the cover button to crouch behind walls or objects).

You can also kill cultists in the room where you first speak to Saverak and free him later.

To conclude the quest, you can either kill Detective Nelly to become an Unholy Assassin, gaining access to an assassin's shop and making it easier to track Orin, or defeat the cultists to obtain the Sword of Chaos and Saverok’s Horned Helmet.

The Amulet of Bhaal can be looted regardless of your choice.