Here is the full list of all 30 The Darkside Detective achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Close case 7: Buy Hard
Fully explore the vents
Play games in arcade
Remember neglected responsibilities
Take a photo at the photobooth
Watch the credits to the end.
Close case 6: Don Of The Dead.
Slack off the job and read a trashy mag in each case.
Close case 5: Loch Mess.
Close case 4: Police Farce.
Give Laxatives to McKing.
Close case 3: Disorient Express.
Close case 2: Tome Alone.
Close case 1: Malice In Wonderland.
Check Roy's Alibi
Listen to all of John's gags.
Examine 8 cars.
Listen to all of Dick Brickman's radio shows. Featuring Dick Brickman.
Use the kango hammer on everything in the sewers before advancing.
Search 10 bins.
Enter the Cursed Lodge.
Read all the book titles in the library.
Complete the virus minigame in three steps.
Spot the Darkside SkyBeast.
Take all of the Turner's calls in the Bloodwolf HQ.