The blacklight map
The GTA 5 Collector's Edition contains a blueprint map with hidden text on its rear side—but you need to use a UV / blacklight lamp to reveal it. You can see the hints in the image below. Don't ask us how anyone found this in the first place ("Ooh, I must inspect that with an industrial UV lamp I had lying around...")—but it's possible they add another layer to the puzzle. Many clues relate to hidden spaceship parts that you need to collect to obtain 100% completion, but some are more abstract.
For example, the prison near Sandy Shores is circled, with the words '9A'. This almost, but not quite, matches a hotspot from the mural map, so it could be an alignment issue—but we don't know. Either way, when you fly into the prison, starting an instant four-star wanted level, you can see detention block 9A in the middle. We've explored it repeatedly and can't find any hidden entrances, but some say there is a scrawled clue for a graffiti part. More likely, block 9A relates to another—possibly related—conspiracy theory about a mass murderer.
The mass murder mystery
There's a poem you can find in the national park that relates to the serial killer and note pieces. It says:
One is done
Two was fun
Three tried to run
Four called mom
Fives not alive
Six is nix
Sevens in heaven
8 won't wait
The inference is that each entry relates to a murder victim. There's another set of writing in the national park. It says -
They want me. They can have.
But they'll never get my people.
Even though I shall leave them sign enough.
Where they put me.
This reads like the final confession of the killer. But where did they put him and what signs were left? The belief is that they put him in prison cell 9A where there's another note on the wall that you can read below.
Note the scrawled half-finished '8s' that look a bit like the UFOs on the blueprint UV map (possibly a co-incidence), plus the drawing, which very closely resembles the far north tip of Los Santos and its islands. The text clearly references a volcano, but the 'infinite eight' bit deserves further inspection. Is it 'infinite' as in eternal or undead? Does this reference UFOs, or some form of cult like the Epsilon Program or the Illuminati? Are they aliens or cult members sacrificed for some higher goal? We don't know, and it might be a separate mystery—but it needs to be solved.
The Vinewood movie murder mystery
Another murder mystery has been discovered in the new-gen version of the game. Here are the details, courtesy of GTA V O'clock.
Keep your eyes peeled. There may be more secrets squirreled away in the PC edition.
So, what's next?
We need to find the remaining two (maybe three) clues on the mural map, which might be further UFO sightings—or something else. These may require the use of specific characters, and unique circumstances (e.g. weather or time, like the hologram). One theory is that a character needs to be abducted by the UFO above the Sandy Shores monument, since this UFO has a hatch that opens and closes, with glowing lights. In-game radio makes reference to UFO abductions, plus there are graffiti hints.
There's also a weird clue on the blueprint map, with the words 'Shoot for the stars' next to the UFO-shaped squiggle. Perhaps you literally shoot at the stars from this location with a sniper rifle (previous GTA's let you shoot the moon and alter its size). Or perhaps the solution is more oblique, and the stars reference celebrities. Do you have to target a celebrity who's part of a cult?
We need you!
Either way, the hunt is on to solve GTA 5's grand mystery—and we'd love to do it first. We'd love to see or hear your thoughts, pictures, videos and suspicions below. It's possible we're all wrong, and the mural map is being misread—but the UFO sightings are real, and the locations do tie up with their position on the map.
Some think that solving the puzzle will unlock a sliding door in the cable car station, revealing the jet pack or an underground lift. Others say the jet pack might be needed to find the final puzzle piece. Others say that there's a secret underground world under the map. Madness, surely—but given the level of attention and detail in GTA 5, plus how keenly Rockstar would have tracked the conspiracy trails in GTA: San Andreas, we're ruling nothing out.
So: get hunting! Let's crack this thing!