Telika, could you please edit your post and add a link to this post? And mark that a clear solution is given here. But the fact is that by asking a lot of questions you have indeed solved the riddle.

So here we are: the easy thing is to notice that Lisa is not able to lift a half barrel keg (that's more than 70kg) and since Jack was addressing a single person we may assume that she is innocent and hence the question: whose footstep did she hear? It could be either Peter or Matthew. The second one is less probable but can you be sure about it? Yes, and Telika provided the proof! Perhaps I overdid when I described the conversation between Matthew and Jack (I made it too obscure) but it was a very short one. Matthew only asked Jack whether he is fine and Jack said that it's ok. And the alarm went off immediately so we are talking about a few seconds. The security system only allows you to open the door and close them immediately. And that means that after the crash Matthew "ran there as fast as I could" and he was only able to see that Jack was murdered before the alarm went off again. It was not possible for him to run through the whole facility and being heard by Lisa. So it had to be Peter and since Anna is trying to cover him up it means that both of them are guilty. I'm aware that there were several answers like that but they lacked one thing: a clear proof that it couldn't be Matthew.

I may also mention that I didn't want to give you the exact measurements of the facility because I was afraid that it would be too suggestive. But I think it is safe to assume that a workshop cannot be a small room but with a side of at least half a dozen or so meters. At least all scientific facilities that I've seen have a large workshop.

If you feel that the riddle is not very logical please do not hesitate to say so. I always appreciate a constructive criticism - as I said befor I've never claimed my riddles to be perfect and hearing about their weaknesses makes me creating better ones in future. Or at least should make me ;)

Yay !

But I don't understand why the killer has to be Peter. I'm certain Anna would have been perfectly able to lift the weight too (and to make noisy steps). Also, I didn't provide a mobile (well, I did, but it would make Anna and Peter the dumbest criminals ever, which, after all, may be the case). What was supposed to stay between them, and be warrant of a premeditated murder ?

(Also I'm very disappointed that it didn't take place in a piano factory.)

Congratulations Telika. I was working on a similar theory but I had to leave for a moment and when I return I see you found the solution.

Thanks again Ghorpm for creating this contests.

I would trust Lisa in that matter. If she said it had to be either Peter or Matthew let us believe her. They were wearing heavy boots (there were guards after all) and Anna was probably wearing more comfortable and smaller shoes. But actually if you think about it... it doesn't matter at all, because they are both guilty ;)

You were never required to explain the motive and I deliberately didn't provide any. I thought that Anna and Peter's guilt seemed to obvious so I decided to give a clear motive only for Lisa and Matthew. However, I didn't manage to fool anybody ;) I will not reveal the true motive because I found it quite amusing and I will probably use it in some other riddle.

Damn! I should have thought about it!
Better luck next time. And I think you will not have to wait for such a long time for a next riddle. I already have a pretty idea although I still have to work on it a bit.

Ohhhhnooooo!! Can't believe I missed this one! Many thanks anyway Ghorpm, the effort you put into this is impressive and appreciated! +10 :-P

I would have tried this. If i didnt get bored reading the long text....

Sooner or later you'll get your chance! I prepare next mystery ;) I already have a "catch" but I've recently realized it has a flaw so I still have to work on it.

Thank you! ;p

I've promised you a new contest but unfortunately I'm awfully busy at the moment. The story is ready but I don't have time to post it and answer all replies so please be patient. The Case of the Ghost will show up... eventually ;)