All riiiight then....
Gumshoe was killed with a trap. Specifically, a machine in the robotics room was used to stab him. Programming it in advance to do this would be possible if one of the others had gained access to Blue Screens before. We know that someone must have had prior knowledge, because someone had to send the invitations.
Is it clued that anyone has been there besides Lisa Basil? Somewhat. The container of adhesive, as far as I can tell, was unlabeled, so Larry Butz should not have known what it was. He only picked it up for two reasons: to conceal the fact that he had a knife (since the container could explain the alarm) and to create an alibi.
However, this alibi was false. The adhesive remover works as fast as the adhesive. It is possible that Lisa returned with the remover, and went to replace it in the storage room. Larry then stabbed her in the room, and restuck himself to the floor.
Creating the final scene - strangling himself - is trickier. He had to use a robot: Maya Fey. She is not a person who kills, but rather a murder weapon, as she is an android. Here are the clues.
First, she is not described as "dead," but as having no pulse.
Second, it is possible that she set off the metal detector.
Third, she is able to tell that ramen noodles are microscopically round on examination.
So to make the final scene, Larry used Maya to strangle himself after killing Edgeworth. There is no rule that Maya cannot be a robot - we only have in red that she is CALLED Maya Fey.
In that case, the final, fifth person in the building, in red, was the dead Gumshoe. The red truth stating five persons did not say five LIVING persons.