Everything that has written here are all tested on Death Wish by myself, so all these things are possible to do.

SKILLS

Since I'm trying to show you the way of sneaking this map, you better use your stealth skill set. If you'd like to check out my own stealth build then there are the Skills[pd2skills.com]

PERKS AND WEAPONS

Use burglar
Weapons can be anything that would give you around 3-6 detection risk. CAR-4, USP (Interceptor),
Chimano Custom Pistol, Deagle, B9 and such. You'd better not take a knife with you because it's pointless, it only increases your detection risk. But if you really wanna bring one, then choose Nova's Shank.

PREPLANNING

Deploy a Body Bag to the Renovated Exhibition Room.
Deploy a Thermite Paste to the Forecourt.
Deploy a Bag Man to the East Staircase Window.
And deploy a Cutter.

These are all necessary. They might cost a lot, especially if you're doing it on Death Wish difficulty but believe me friend, they will be super helpful.

As soon as you spawn, you'll automatically get the cutter so go and get a termite paste. So now, going straight and using the main door is risky cause of the guards. Take the left path and try to reach the building's wall. You'll see four windows and you'll apply termite paste to any of them you want. And then you'll pick the window's lock and get in. Making the entry is that easy but watch out for the cameras nearby the windows because they'll surely detect you before you can ever finish picking the window's lock, even if you have the lockpicking skill. So use your camera loop or your jammer. Or just hope that there wouldn't be any cameras.

Four Windows can be seen in the picture

SECURITY ROOM

Inside, there will be lots of rooms you can check out. The one that has the "Security" sign at the top of it's door is where the camera man stands, spawns randomly. It would be super great if you can kill him. Otherwise you'll be having so much pain.

ALARM BOXES

Just like the original Diamond Heist from the first PAYDAY game, there will be alarm boxes you must find. They are randomly spawned but most probably they are in the rooms. Some rooms are empty though, you can use them to hide the bags and hostages. Alarm boxes don't have to be in the rooms either, anyway. So check out the walls and you'll find them. You will need to hack only four of them but I'm sure more than four boxes will spawn.

DOORS TO THE VAULT

When you're done with the alarm boxes, you'll now need to find keycards. As far as I've experienced the guards don't have cards but all the civilians have. So tie down the civilians and take keycards from them. You can hide them in the empty rooms because the guards don't check them.

First door
The first door will be marked on map, go there and insert the keycard. It also has a time lock, don't worry though. When guards see them, they don't alert. Time lock can't be stopped either so chill. Time lock is 1 minute and 30 seconds (on Death Wish at least) By the time, try to tie down another civilian because you'll need another key.
When the door's open, there will be a room and there will be max. 3 guards inside, don't even mess with them. Go straight and insert the other keycard to the 2nd vault door.

Second door
Guards don't care about this door, either. Even though sometimes they stand in front of it and see it's opening but what they do ? Nothing.
When the 2nd door's open, there will be the last door you'll need to pick. And then you'll be done with the doors.

TILES

So, here comes the tricky part. When you're at the vault, you'll see tiles on the ground. Don't step on them yet. There will be a box at your left you'll need to use. This box will generate a safe path for you to use, so you'll be able to pass the tile part.

The green lights in the box are showing the correct tiles, so if you step on the wrong ones then whole mission will screw up. You'll have 30 seconds (on Death Wish) to pass the tiles, get the diamond and get back. The tile code will be random every time so you better hurry up, especially if you're doing it on solo.

The lights in the box show you the tile code, you'll have to memorize it.
The green lights are marked with the red crosses.
And this is their places on the tiles.

CUTTER

Once you're done with the diamond, I suggest you to get rid of it right away so you'll be able to look for the extra loot in peace, without pressure. That's the part where cutter becomes useful. The whole stuff you saw during the time you were hanging around the map can be taken. Some of them actually, the ones that has the GenSec sign on them. You'll be able to cut their glasses and take them.

You could have done this before you stole the diamond but the reason I'm telling you to do it now because I thought you wouldn't wanna get busy with the stuff yet. After all that search, your effort can be burnt by a single mistake you can do in the vault. So first secure the diamond and then look for the extra loot later. Even if you get detected now, you'll be able to escape at least and get an achievement if you haven't unlocked yet.

As a result, I guess you can find max. 10 items to collect. So if you secure 10 bags plus the diamond and finish the heist, you'll unlock an achievement.

When you're all done, you can use the other termite paste to open a window at the basement to make a safe escape. If you didn't take the other paste, then just use your jammer and rush to the van using the main door.

MONEY

The diamond will worth $6.150.000 and a single loot bag will worth $205.000. If you take all bags plus the diamond, I guess you'll never need to stealth for money again.

I hope this method of sneaking was helpful. It's not easy though, especially not on Death Wish. But still the safest way. Doable at least.

If you have anything to add, any thoughts about the guide, anything you wanna say just post it to the comment section. Your feedback is important for me and thanks for reading this guide.
You can check out my PAYDAY: The Heist Diamond Heist Stealth Guide as well if you'd like to.

ALL SCREENSHOTS, TEXTS AND ANYTHING ELSE MADE BY- The Evilator