引用自 CaulSans 「ビクトル」：

http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1189378447 Laptops locations with Map.
Security Room locations with Map.

Difficulty: Overkill or above.
Mode: Loud or Stealth.
Description: On the Diamond Heist secure the red diamond on Overkill difficulty or above.

• Tip: On the difficulty Mayhem or above, the spawn rate of Red Diamond vault is increased.
  
• This achievement is based on "luck", when you open the first vault, there's a chance to the second vault with Red Diamond spawn.

Note: To receive the achievement, you just need to secure the Red Diamond. The heist don't need to be completed.
The Second vault.
The Red Diamond.

Difficulty: Overkill or above.
Mode: Stealth only.
Description: On the Diamond Heist find and pick up every sapphire outside the vault on the Overkill difficulty or above.

• Tip: You can make it while play the heist or make an ECM Rush just to get them. But it need to be made only on Stealth.
  Note: You can make an ECM Rush solo (2 ECMs MAXED) or you can make it with a friend (In this case It's recommended max the ECM too).
  
• The spawn of the Sapphires is static, so you can memorize or use the map below to get them.
  Note: To receive the achievement, you just need to get all Sapphires. The heist don't need to be completed.

Map Caption:

• Blue dots: Sapphires on 22 Floor.
  
• Green dots: Sapphires on 23 Floor.
  
• Red dots: Sapphires in vault area.

Sapphire 1 (22 Floor)
Sapphire 2 (22 Floor)
Sapphire 3 (22 Floor)
Sapphire 4 (22 Floor)
Sapphire 5 (22 Floor)
Sapphire 6 (22 Floor)
Sapphire 7 (23 Floor)
Sapphire 8 (23 Floor)
Sapphire 9 (23 Floor)
Sapphire 10 (23 Floor)
Sapphire 11 (Vault area)
Sapphire 12 (Vault area)

Difficulty: Normal or above.
Mode: Loud only.
Description: Steal from the Dead.

• When the alarm trigger, you'll need to escort the CFO to the roof. When Bain get the master code from him, he will be throwed away on the vault fountain. Climb the fountain and get the money bundle that he dropped.
  Note: To receive the achievement, you just need to get the money bundle. The heist don't need to be completed.

Blueprint of Diamond Heist:
Reddit Post.

Thanks to:

• Jelaruk - For helping me manage this and my another guide.

Thanks for reading.
Any errors on the guide, use the comment section please.