Alien Swarm: "Who scores the kill if ... (collection of cases)?"

_{This is a collection of questions like "Who gets the kill if someone does this and someone else does that?"}
^{Includes sentry, barrels, flamethrower questions, as well as questions about various offhand items.}

1. Do sentry kills count as kills?
   
   Who scores the kill if...
   1. ...someone brings a sentry to the mission and someone else assembles it?
   2. ...someone brings a sentry to the mission, assembles it and then someone dismantles and assembles it again?
   3. ...someone brings a sentry to the mission, starts assembling it, but someone else finishes it?
   4. ...the sentry was brought by someone and assembled by someone else, and then rotated by another person?
      
      
2. 1. If an alien dies because of the explosion of a barrel you shot, does it count as a kill?
   2. If you shoot a barrel with weapon, and an alien dies, does that count as weapon kill?
      (i.e. for achievements)
      
      
3. 1. If someone sets an alien on fire, and then someone else attacks it with flamethrower again (on Easy difficulty, for example), whom does the kill count to?
      
      
4. Are kills with the following offhand items counted?
   
   
   1. Hornet Barrage
   2. MTD6 Smart Bomb
   3. Hand Grenades
   4. Assault Jets
   5. v45 Electric Charged Armor
   6. ML30 Laser Trip Mine
   7. M478 Proximity Incendiary Mines
   8. IAF Tesla Sentry Coil

Partial answers are also good.

Solution 1:

1. Sentry kills do not count as kills!

2.1. Yes, barrel-kills are counted
   2. No, they don't count as a weapon kill.

4. Offhand items:

   Hornet Barrage    ✓ Yes
   Smart Bomb        ✓ Yes
   Hand Grenades     ✓ Yes
   Assault Jets      ✓ Yes
   Electric Armor    ✓ Yes
   Laser Trip Mines  ✓ Yes
   Incendiary Mines  ✗ No
   Tesla Sentry Coil ✗ No