The problem on Elite Mode is you basically have to arrest every suspect on the map, which inadvertently neuters your sniper(s) if they have a shot. If they do take the shot it will be a legal kill in game, but you will not be able to complete the mission and pass on Elite Mode.
From the Wikipedia entry: On the most difficult level, Elite, players need a 95/100 to pass, and will fail for killing even a single suspect, losing more than two team members without committing an infraction, or committing any infraction in addition to being injured.
I wish I would have known that early on as I took several sniper shots and completed the mission, only to be presented with scores that did not pass. The most aggravating was when I had a 93/100 and would have passed had I not taken out a suspect in a hallway with a sniper.
The other part of this equation is that in taking all of the suspects alive, you essentially are limited to non-lethal weapons and flash bangs. You do not want to kill a hostage with a shock from a stinger grenade, and you don't want multiple lawful kills on suspects (or any kills).
Those factors make SWAT 4 a bitch to play and also a very enjoyable tactical game. While there are some issues with the game itself, it is one of the most playable tactical shooters out there and would be tough to beat in terms of content by anything out their currently.
Other thoughts: It is better to have your teams covering a door, while you open it from the side. This lets them see inside the room and call out targets (and they will auto-engage/pursue) without you risking them on a breach/bang/clear scenario.