Kill target quickly with remote mine on "A New Life"
Get the donuts from the food truck and inject them with poison or sedative, then drop them outside the "undercover" FBI truck. Wait for them to die or pass out, then change into the FBI clothes and run up to the front of the target's house. There is a window in front, to the left of the main door. Look through it to see a small table with a cell phone. Making sure nobody is looking, place a mine directly on the window (select the mine, enter first person view, then press Fire while aiming at the window). Run back to the FBI truck and use the computer inside to call the target. When he walks over toward the window to pick up the phone, detonate the mine. The explosion will go through the window and take out the target. If you do this fast enough, it will not matter if an FBI agent notices the mine and goes to investigate as he will also be caught in the blast. Your tension meter will remain at yellow until you finish the level due to the explosion. However, as long as you do not do anything really crazy, you should be fine. Use the lighter fluid/grill trick to get the necklace from the wife and you can get through the mission in under ten minutes.