I cant't get the handcuffs on the guy before he attacks in the courthouse or city hall or whatever. I pull the gun, command him to kneel, but he stands as soon as I exit the inventory with the cuffs no matter how fast or slow I react. Is this a known glitch? Will re-installing help?

Funnily I just had the same issue.

I found out that the game gives you 7 (DOS)/10 (Windows) seconds after he kneels down, BUT that time counts down EVEN if you are in menus like inventory.

So you need to be very fast especially in inventory.

In ScummVM we are probably fixing this, so that you have less time, but game menu + inventory time won't count.

Sierra had provided a patch to fix this handcuff issue. I am having the same issue. I am not getting 7 seconds to cuff regardless off everything.

Using windows 10. Anyone got any ideas?

Did you try playing the game with ScummVM? Is the issue there too?
Looking at our code for the SCI engine, there is a patch implemented for this case (and a few other similar ones), so it should be fixed in a recent ScummVM release (or a daily developer build).