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
Examine 8 cars.
Watch the credits to the end.
Close case 6: Don Of The Dead.
Use the kango hammer on everything in the sewers before advancing.
Search 10 bins.
Slack off the job and read a trashy mag in each case.
Close case 5: Loch Mess.
Enter the Cursed Lodge.
Take all of the Turner's calls in the Bloodwolf HQ.
Close case 4: Police Farce.
Listen to all of Dick Brickman's radio shows. Featuring Dick Brickman.
Give Laxatives to McKing.
Close case 3: Disorient Express.
Complete the virus minigame in three steps.
Listen to all of John's gags.
Spot the Darkside SkyBeast.
Read all the book titles in the library.
Check Roy's Alibi
Close case 2: Tome Alone.
Close case 1: Malice In Wonderland.