This walkthru will help you to finish "Witness". Okay, you start South of the house, where you just picked up a matchbook. Go North twice to the front door and ring the bell. Phong will let you in.
Then just try to go East, and Phong will lead you to the Living Room, where Monica and Mr. Linder are. Now, wait (get used to doing that, because there's a lot of waiting in this one), and Linder will eventually take you to his office. Sit down in the wooden chair, and Linder will hand you a note. Read it, as it will help waste some time. Now, just do anything (but stay seated!) to make time pass. Show the matchbook to Linder for an interesting reaction, if you like. In any case, you just have to keep waiting.
Eventually, Monica will come in briefly to announce she's going to the movies. This is not what you're waiting for, however! So, keep on waiting, and finally, the murder will occur. Linder will be shot while you sit there, and you can't stop it from happening. Read the description carefully at the moment the shot is fired. There's something odd about it. In fact, the whole thing is a setup.
The first thing to do is stand up, then push the button. Instead of ringing to summon the butler, it causes a strange click to be heard from the clock. At this point, Phong will enter the room. Tell him you want the keys, and he'll hand them over to you. Now, examine the clock. Keyhole seems a little strange, doesn't it? The doorbell rings while you're doing this, so as Phong goes to answer the door, examine the keyhole.
I'll bet you're getting some ideas already! However, you'll need to have the powder analyzed, and Duffy hasn't arrived yet, so wait around until he does. Then get the powder analzyed (you can ignore Stiles, he's only a red herring). While that's being done, examine the window (you can't open the clock yet, it's the one key you don't have). The green wire seems suspicious, so get it for future reference.
Now, go West into the Hallway, then North twice, and open the Butler's door. Go West into the room, and read the mystery book (by the way, you can drop the telegram and note, they aren't important). A gun receipt is used as a bookmark. The purchaser's name is obviously phoney, but hang on to the receipt anyway. Okay, from the Butler's Room, go East twice to Monica's room, then unlock and open the back door. Go East into the Backyard, then South twice to the office path.
Aha, a muddy gun! No fingerprints, alas, but you might want to take it along with you, just in case. Now, go West into the Side Yard. Hmm, more footprints here, but they aren't quite the same as the ones on the office path. In fact, it looks like someone was standing here for awhile. Wonder who it might have been? (No, *not* Sergeant Duffy!). Anyway, go West again to the driveway, then North and East into the Garage. Unlock and open both the garage door and the workshop door, then go East into the Workshop.
The place looks like an electrician's paradise, and there isn't much you can do here; but, there are spools of wire hanging around. Could it be...? Examine spool, and you have established a link of sorts between this place and the study. The green wire is obviously from this room. Now, all you need is the person who put it there.
You now stand there waiting for Monica. Just keep waiting; she'll arrive (saying "Wait for Monica" is easiest. It will take a while, so if you want to hunt down Phong and ask him about the gun receipt, you have time). When she does get there, she'll fiddle briefly with the junction box (very suspicious!) before noticing you. Now, wait until she leaves, then follow her. You *must* use directions here, just saying "Follow Monica" won't work. Follow her all the way to her room, and wait for her to come back out of the bathroom. When she returns, ask her about Mr. Linder.
Her response will establish the motive. Now, wait some more, and she will eventually leave the room. Follow her again, this time to the office. As soon as you get in there, handcuff her. Somewhere along the way, Sgt. Duffy will have left with the body, so you can't arrest her until he comes back. In the meantime, you have to find some very important evidence. So, first search Monica for the key. When you get it, unlock the clock and open it. She's already removed the gun, but you can search her for that, also.
Now, just wait until Duffy returns, and arrest her for the murder. And that should be about it. By the way, if you try leaving her and waiting in the office (so you can find the gun in the clock), you'll find that, however hard you try, you won't be able to handcuff her (which is necessary so she can be searched). So, you'll just have to wait and follow her. As I said in the beginning, it's a pretty simple game.