ok i put it on my "have a closer look at it" list, looks certainly atmospheric :)

I won't retype my list, but I will repeat my suggestion of the Infocom text mysteries and the Pastel Flash games.

Infocom because it's the closest you'll get to a classic murder mystery short story in interactive form, full of clues, interviews, confronting with evidence, and deducing who was where when.

Pastel because of these two titles.
http://www.pastelgames.com/index,games,flash_game,65.html
http://www.pastelgames.com/index,games,flash_game,83.html

Legally, you'd have to find an old copy of Lost Treasures of Infocom or a similar bundle, or turn up original disks at a garage sale. Might not be worth the trouble if you're not interested in other text adventures.

Better would be playing all the other games on your list, watching to see if more Infocom games turn up on Gog in the future.

This one is an in browser game, came out a month ago; could check that out..?

http://mediacenter.dw-world.de/english/video/#!/319311/TwinKomplex_a_social_game_with_real_actors

don't know if you can pick your own team though, but still, seems nifty?:

Still a couple of Sierra ones not mentioned - the Laura Bo games - The Colornal Bequest and... the other one! They're not great though
There was KGB /Conspiracy too but it was very hard and unfair - it liked putting you in unwinnable situations randomly and you had to be at the right place at the right time all the while!
At a push you could say that the Broken Swords are investagative, in a Dan Brown / Da Vinci Code (before there WAS a Dan Brown / Da Vinci Code) kinda way

Good call, I believe you mean The Colonel's Bequest and Laura Bow: The Dagger of Amon Ra.
While I haven't finished the second one, I would say that the Colonel's Bequest is very good (albeit old school, and text commands can sometimes take time to figure out), but it's one of the few games where the story develops independently in real time and you need your detective skills to measure up to the evolving situation.

Fahrenheit (Indigo Prophecy) would be another game to consider, though you play both from the perspective of detectives and the criminal.

Another one worth a look would be Bureau 13, where you can choose two different characters and your style of play depends on their talents. The sci-fi universe is based on an RPG and a series of books. I don't know where to find it now though.

I played through Jack Orlando - average at best in my opinion, you would definitely do better with the above and what others have already suggested (GK, PQ, Tex Murphy games etc.).