Saw

This is best done in Chapter 4. You'll get a schematic for it right after you are abandoned. The workbench is in Chapter 4-3. There will be three doors and the workbench is in the far left one. Make the Gas Mine.
Then find a minion, beat him up a little, select the Gas Mine (RB), enter combat stance (LT), and drop the mine (RT). If you need to, lead him into it. If he dies, you'll get the achievement. If you happen to die with him, you'll still get the achievement.

Chapter 4-1

Load up Chapter 4. You will find the schematic on a desktop in a room after you left alone, hard to miss. A little bit later you will reach Chapter 4-1 (door closed behind you, left side is a board on the wall without labels, right side is a reception). Right after the start go to the reception and you can find the required paint and fuse in the file cabinets. Next follow the main path, you will be in a long corridor with 3 doors on the right side, but only the last opened (Room number 107). Inside there is a brokeable wall in the front of you and you can hear an enemy from the right room (watch for the booby trap). Do not disturb the guy, just go through the wall. Kill the enemy with gun collar you will meet on the stairs and disarm the booby trap upstairs. Don't go forward through the gate! Double left, follow the path and jump into the hole in the floor. Kill the enemy there then you can leave this room through the toilet. In the toilet you will find a worktable, so you can make your gas trap. Unbolt the door, go through the wall again and place the gas mine on the left. Use button to choose trap, next Hold then hit . You will see it on the floor. Drop your weapon to make sure you will not kill him, use button. Disarm the booby trap, hit the guy a few times, then go back with him to your trap. He is a little bit shy when on low health, but you can trick him into the trap.