After you’ve entered the crime scene, you have to find the treasure.
Walk north and climb the stairs. Use the door on the right to enter the corridor. Notice the empty frame on the wall. Next to in on the right is a picture with trees. Walk to thei right past that picture to find the same picture upside down. Take the upside down PICTURE and walk back to the south to the empty frame.
Use the upside down picture on the empty frame left of the door and you’ll hear a click. Walk back to the left to the main hall and at the top of the stairs use the door on the left. Use the door on the right of the bookcase to open the closet. Take the PIPE out. Use the door left of the bookcase to enter the kitchen. Take the PAN from the bottom shelf on the left side. Walk left to leave the kitchen. In your inventory use the pipe with the pan and use the combination on the wall to break through.
Use the hole to climb through. You must follow the line connected to the top red button to see it’s leading to the lower right one. Use the button and a key is revealed. Pick up the KEY and leave the room. Use the key on the door on the left to enter the bedroom.
On the shelf is a book that you can’t reach. Take the PILLOW from the bed and use the pillow on the book to knock it on the bed. Take the BOOK from the bed. Walk to the right to leave the bedroom and to the south to return to the kitchen. Walk south again the to the hallway. Use the book you found with the bookcase to turn it around and it takes you to a maze. Stay on the south side of the maze and you should be able to get to the other side. You’ll hear another click.
Walk south to the main hall and at the top of the stairs use the door on the right. In the corridor with the paintings use the door between the paintings. In the next room you will see a Mondriaan-like painting. Use the painting three times to knock it from the wall. An airduct is revealed. Use the duct to get to the room next door and take the HAMMER. Use the airduct again to return. Walk to the right to get to the corridor and walk to the left to reach the main hall.
At the top of the stairs use the door on the left and in the corridor use the door left of the bookcase to get to the kitchen. Walk to the left and use the door on the left to visit the bedroom again. Use the sledgehammer from your inventory on the window and climb out. On the roof you will find a skylight. Use it to remove the cover and use it again to climb through the skylight.
You need to pick the right symbol to put in the empty square on the bottom line. Press the ‘6’ and the door to the vault will open. The treasure is yours.
Game source: A copy of the game was found here on the internet.