I'm having a problem regarding narration and character claims. If we sum up everything said in narration and by characters, then we end up with a total of 7 gunshots happening: The
2
gunshots that killed Nettle and Brian, the
1
gunshot that happened during the police siren that killed Ruby, the
3
gunshots Tom heard, two of which killed Steve and Menna while the other one is unknown, and finally the final
1
shot that killed Alpha.
Both Tony and Tom checked Alpha's gun at the end, and it was fully loaded. Alpha said his and Ren's guns were identical, which means each have space for 6 bullets, so where did that seventh shot come from?
Since two out of the three characters alive at the end confirmed this, I'm certain at least one of them is telling the truth, else they would have killed Alder right there because of the more culprits than innocents red.
So... how did seven gunshots happen if each gun only has six bullets and one was fully loaded?
...At this point, I'm certain Alder is the culprit. There's one viable theory I can think of to get around the gunshot problem, and that is that one of the old bodies was re-used in place of Ruby, while Ruby was killed and put elsewhere. Meaning Alder lied about hearing a gunshot during the siren.
Alternatively, Alpha lied about his and Ren's gun being identical when the truth is either his or Ren's gun has more bullets. Or if we assume Alpha lied again, there's more than two guns.
That said, let me help my dear number friend with his theory.
Alder and Alpha are the culprits.
Before anything, the two got into Miles' room and stole the documents. I don't know why they would want them, possibly hired by someone?
For the first murder, they claim to have been together. However, that is not the case, as Alder just lied to give Alpha an alibi. Alpha went over to Ferris' office while Catherine was in the bathroom and stabbed him to death. After this, he locked the door with his master card key and left. When he reached Alder, Alpha gave him his master card key for the next locked room.
For the second murders, when Alder stormed off he found Micah and Nik. He led them to the closet and stabbed them both, locking the door with the Alpha's master card key afterwards when he was out.
For the third murders, Alder left the conference room with Ruby at one point. Ruby's purple of "Alder called me over" implies Ruby was not with him when he called her, so Alder just got into the security room and stabbed Ren and Miles to death. After this, he took Ren's gun, deleted the security footage and called Ruby over to the crime scene.
As this happened, for the fourth murders, Alpha got out of the conference room and quite simply shot both Brian and Nettle with his own gun.
Alpha lied about no one having Ren's gun, because his partner in crime had it.
At this point, secretly while everyone else was distracted/doing something else, Alder gave the master key card back to Alpha, and Alpha swapped his gun with Alder's (because Alpha's gun has space for more bullets, while Ren's only has 6).
For the fifth murder, Alder had possibly set the sirens to play at one point, and he used this chance to say he had heard a gunshot to go over to check on Ruby. He entered the room she was in and shot her with the gun he had been given, then left.
The door was not locked, so Alpha just opened it.
For the sixth murders, Alder separated from the group, lying when he said he was going to the conference room. When he saw his soon to be victims, he shot them both. Catherine, who was in her office, rushed out, but she was shot too. Alder quickly pushed her body into her office and went to hid in the room closest to him: Ferris'.
He lied when he said Catherine was stabbed to death. Honestly, he had me fooled there.
Finally, at the end while Tom and Tony were distracted, Alder gave Alpha's gun back to him. And so, Alpha went over to Tony's room. There, he locked the room from the inside, shot his own gun at the ceiling and hid it in the room.
After this, he laid down on the floor and faked death. When Alder arrived, he lied about him having been shot and about him being dead. The gun Tom and Tony checked was Ren's, which had not been used at any point, so no contradictions were made.