Helicopter Crash

The Helicopter Crash was an event that occurred during the Christmas Eve incident, which led to the murder of a SWAT sniper aiming for Batman, and the shooting down of the SWAT chopper Air One by Deadshot, one of the eight assassins after Batman's head.

Before Arkham Origins Incident
Sometime after the Joker took over Black Mask's operations, Joker proceeded to hire eight assassins (Deathstroke, Copperhead, Firefly, Bane, Electrocutioner, Lady Shiva, Killer Croc, and Deadshot) with a bounty of $50 million on the vigilante Batman's head.

Arkham Origins Incident
After Howard Branden's SWAT team learned of the hit on Batman by "Black Mask", they decided to cash in and try to get the bounty by killing Batman. One part of the SWAT team sent in a dummy distress signal at the Bowery to lure Batman over to the location, then send a chopper, codenamed Air One, to stun Batman long enough for a SWAT sniper in position to snipe Batman. However, one of the assassins, Floyd Lawton, aka Deadshot, not wanting anyone to steal his bounty, utilized his sniping skills to simultaneously take out both the SWAT sniper (thus effectively saving Batman's life again) and shooting down the SWAT chopper. He also made sure his spent bullet casing contained his frequency specifically so Batman could contact him. Batman, witnessing the event, managed to deduce Deadshot's involvement based on the trajectory and ricochet effect (a trademark of Deadshot) after investigating the event.

Casefile details
SWAT: This is the Police. If you fail to comply, the use of deadly force has been authorized. (bam) What the hell!? Dispatch, Air 1 is hit! Repeat - I'm going down! Mayday! Mayday!

Batman: I'll look for survivors. No survivors. Someone will pay for this. I need to set up a crime scene to find out who.

Scan of the pilot's corpse "DNA Evidence Impact pattern Analysis: Victim killed by impact Cause of death: Broken neck Speed of impact: 79 km/h Victim weight: 75 kg Angle of impact: 34 degrees Impact radius: 56 cm"

- Impact pattern scan results for victim

Batman: The helicopter was spinning out of control. The pilot was killed on impact - not by the gunshot I heard. But what caused him to lose control? Maybe I can learn more back on the rooftop.

Scan of first point of impact

Batman: I can analyze the first point of impact from here.

"Trace Evidence Impact Pattern Analysis: Impact severed helicopter tail Impact force: 1168 Newton Speed of impact: 42 km/h Tensile strength: 248 MPa Angle of impact: 14 degrees Impact radius: 23 cm"

- Impact Pattern scan results from first point of impact

Batman: The helicopter's tail rotor was severed when the fuselage hit the building. I should review the crime scene and find that tail rotor.

Scan of the severed tail rotor

"Bullet Impact Trajectory analysis Analysis: Bullet impact disabled tail rotor Projectile caliber: 12.7 mm (.50) Impact energy: 2802 ft-lb Breach diameter: 56mm Angle of impact: 19 degrees"

- Bullet impact scan results from severed tail rotor

Batman: The helicopter crashed when a high-powered round shattered the tail rotor. Ballistics analysis will lead me to the shooter's position.

Scan of the downed SWAT member

Batman: This doesn't add up. This man is a member of SWAT. So why did he fire on a police helicopter?

"DNA Evidence Impact pattern Analysis: Bullet impact from behind Bullet caliber: 12.7 mm (.50) Impact energy: 2802 ft/lb Breach diameter: 56mm Angle of impact: 19 degrees"

- Impact pattern scan results for downed SWAT member

Batman: This man didn't fire at the helicopter - he was aiming at me. The ballistics trace indicates this officer was killed by a ricochet from the same round that took down the chopper. There's only one person capable of a shot like this - Deadshot.

Conclusion

Batman: The trajectory analysis will lead me to Deadshot's firing position.

Trivia

 * This is technically the second time Deadshot saved his quarry from a rival assassin, after the Batman: Arkham Origins debut trailer (where he interfered with Deathstroke's attempt on Batman's life).
 * Air One was also one of the choppers deployed at Pioneer's Bridge later into the game. Coincidentally, that Air One chopper also ended up shot down by one of the eight assassins while Batman was nearby to witness it (in this case, Firefly), although unlike the one in this casefile, the chopper isn't targeting Batman, and Batman doesn't have a case file dedicated to it.
 * The Case File was also utilized in the 2013 E3 demo, with the only notable difference being that it occurred close to the Royal Hotel, and that the player was not obligated to locate Deadshot's sniping position unlike in the final release of the game.