I've had a few people asking for this so here it is.

The game requires ALL the clues to be gathered including some clues regarding the Reverend to complete the game (they appear in bold). Typed in commands appear in CAPITALS. The following shows the solutions to puzzles and clues regarding a room or an object:

Greenhouse

X FOOTPRINTS.

Cerebus room

OPEN WARDROBE. GET DAGGER. OPEN CHEST OF DRAWERS. PULL DRAWER. GET LETTER. READ LETTER.

Zeus room

OPEN BUREAU. GET SCRAPBOOK. READ SCRAPBOOK. GET CLIPPING. READ CLIPPING.

Hut

In the Hades room: GET BOOTS. EMPTY BOOTS. GET BRASS KEY. At the lake: GET OARS. USE OARS WITH BOAT. USE BOOTS WITH FOOTPRINTS. UNLOCK DOOR. OPEN DOOR. IN. OPEN TEA CHEST. GET TOWEL. GET CANDLESTICKS. GET ROPE.

Crypt Tomb

In the study: X DESK. USE DAGGER WITH DRAWER. OPEN DRAWER. GET MATCHES. At Rusty Gates: GET SAND. At Oak Tree: X SEAT. GET HACKSAW. At Waxworks: USE SAW ON WAXWORK. GET HEAD. In the Furnace room: USE HEAD WITH FURNACE. USE MATCHES WITH FURNACE. USE SAND ON FIRE. GET IRON KEY. Outside of the Crypt: UNLOCK GATE. OPEN GATE. In the Tomb: X SARCOPHAGUS. Make a note of the 3 numbers. They are the combination to the safe in the secret room.

Secret Room

In the Artemis room: OPEN BOX. GET DIAMOND RING. On the roof. USE ROPE WITH FLAGPOLE. CLIMB ROPE. USE RING ON GLASS. OPEN WINDOW. IN. USE COMBINATION. Type in the 3 numbers found in the tomb. OPEN SAFE. GET DOCUMENT. GET SMALL LETTER. READ DOCUMENT. READ SMALL LETTER.

Towel

In the Bathroom: X BATH. GET SOAP. In the Utility room: USE SOAP ON TOWEL. USE TOWEL WITH WATER. GET TOWEL. X TOWEL. You find initials.

Shoes and Dagger

In the Poseidon room: LIFT RUG. USE DAGGER WITH FLOORBOARD. X HOLE. GET SHOES. In the Greenhouse: USE SHOES WITH FOOTPRINTS. USE DAGGER WITH LORD.

Inventory

Make sure you are carrying the following to complete the game:
DAGGER, BOOTS, SHOES, LETTER, SMALL LETTER, DOCUMENT, TOWEL (clean), and CLIPPING.

Now what follows is the conversations and/or actions with the suspects that will complete the game in the right order of sequence. Other questions can be ASKed of the suspects but they're not flagged as important clues. The command format is ASK (suspect) ABOUT (keyword):

ASK DOCTOR ABOUT ENEMIES.
GIVE SMALL LETTER TO DOCTOR.
ASK SIMON ABOUT CLUBS.
ASK VERONICA ABOUT ALIVE.
GIVE SMALL LETTER TO VERONICA.
ASK LADY ABOUT PERSON.
ASK SIMON ABOUT WOMANIZER.
GIVE CANDLESTICKS TO REVEREND.
ASK REVEREND ABOUT THIEF.
ASK LADY ABOUT ELIZABETH.
GIVE DAGGER TO MAJOR.
GIVE CLIPPING TO MAJOR.

So, to complete the game you need to do all 7 actions in bold. Carry the listed above 8 objects. Complete the 12 ASK or GIVE commands with the suspects. There are 27 things to do in all.

I'll let you work out from all the clues gathered who the suspect is, Inspector. Just POINT TO (and the name of the suspect).

Good luck.

I had already uncovered a good part of the game wih the comments and a bit of curiosity and now ... a complete walkthrough !

However there is somehing thant I don't understand yet.
What do you mean by "Just POINT TO" ?
I entered this command with the name of the suspect.
I though I had just to point to somebody and receive a message like "You're right, Inspector and the suspect starts to run away..." but instead the game didn't return anything at all, not even an error.
I tried it with nearly all he suspects for the same result.

Could you give a more detailled explanation of the solving process, please ?

Thank you very much

The Walkthrough is missing one crucial point, namely to take the clean towel with you from the washtub. If you have all the items with you and spoken to all the suspects, the big reveal should happen automatically in which the detective explains his clues. And then you can point to the person. (It is best to save before you do that).