ボタンを押すとアプリがクラッシュ

Swiftでピアノアプリを作っています。
アプリをビルドし、ピアノの鍵盤をタップすると音が鳴らなく、また、アプリが落ちてしまいます。
ソースコードは以下のようになります。

import UIKit
import AVFoundation

class ViewController: UIViewController {
    var pianoSoundC3 = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("C3", ofType:"mp3")!)
    var audioPlayerC3 = AVAudioPlayer()

    var pianoSoundCS = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("C#", ofType:"mp3")!)
    var audioPlayerCS = AVAudioPlayer()

    var pianoSoundD = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("D", ofType:"mp3")!)
    var audioPlayerD = AVAudioPlayer()

    var pianoSoundDS = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("D#", ofType:"mp3")!)
    var audioPlayerDS = AVAudioPlayer()

    var pianoSoundE = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("E", ofType:"mp3")!)
    var audioPlayerE = AVAudioPlayer()

    var pianoSoundF = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("F", ofType:"mp3")!)
    var audioPlayerF = AVAudioPlayer()

    var pianoSoundFS = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("F#", ofType:"mp3")!)
    var audioPlayerFS = AVAudioPlayer()

    var pianoSoundG = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("G", ofType:"mp3")!)
    var audioPlayerG = AVAudioPlayer()

    var pianoSoundGS = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("G#", ofType:"mp3")!)
    var audioPlayerGS = AVAudioPlayer()

    var pianoSoundA = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("A", ofType:"mp3")!)
    var audioPlayerA = AVAudioPlayer()

    var pianoSoundAS = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("A#", ofType:"mp3")!)
    var audioPlayerAS = AVAudioPlayer()

    var pianoSoundB = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("B", ofType:"mp3")!)
    var audioPlayerB = AVAudioPlayer()

    var pianoSoundC4 = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("C4", ofType:"mp3")!)
    var audioPlayerC4 = AVAudioPlayer()

    override func viewDidLoad() {
        super.viewDidLoad()

        let audioPlayerC3 = try! AVAudioPlayer(contentsOfURL:pianoSoundC3)
        audioPlayerC3.prepareToPlay()

        let audioPlayerCS = try! AVAudioPlayer(contentsOfURL:pianoSoundCS)
        audioPlayerCS.prepareToPlay()

        let audioPlayerD = try! AVAudioPlayer(contentsOfURL:pianoSoundD)
        audioPlayerD.prepareToPlay()

        let audioPlayerDS = try! AVAudioPlayer(contentsOfURL:pianoSoundDS)
        audioPlayerDS.prepareToPlay()

        let audioPlayerE = try! AVAudioPlayer(contentsOfURL:pianoSoundE)
        audioPlayerE.prepareToPlay()

        let audioPlayerF = try! AVAudioPlayer(contentsOfURL:pianoSoundF)
        audioPlayerF.prepareToPlay()

        let audioPlayerFS = try! AVAudioPlayer(contentsOfURL:pianoSoundFS)
        audioPlayerFS.prepareToPlay()

        let audioPlayerG = try! AVAudioPlayer(contentsOfURL:pianoSoundG)
        audioPlayerG.prepareToPlay()

        let audioPlayerGS = try! AVAudioPlayer(contentsOfURL:pianoSoundGS)
        audioPlayerGS.prepareToPlay()

        let audioPlayerA = try! AVAudioPlayer(contentsOfURL:pianoSoundA)
        audioPlayerA.prepareToPlay()

        let audioPlayerAS = try! AVAudioPlayer(contentsOfURL:pianoSoundAS)
        audioPlayerAS.prepareToPlay()

        let audioPlayerB = try! AVAudioPlayer(contentsOfURL:pianoSoundB)
        audioPlayerB.prepareToPlay()

        let audioPlayerC4 = try! AVAudioPlayer(contentsOfURL:pianoSoundC4)
        audioPlayerC4.prepareToPlay()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    @IBAction func C3(sender: UIButton) {
        audioPlayerC3.play()
    }
    @IBAction func CS(sender: UIButton) {
        audioPlayerCS.play()
    }

    @IBAction func D(sender: UIButton) {
         audioPlayerD.play()
    }

    @IBAction func DS(sender: UIButton) {
         audioPlayerDS.play()
    }
    @IBAction func E(sender: UIButton) {
        audioPlayerE.play()
    }

    @IBAction func F(sender: UIButton) {
        audioPlayerF.play()
    }

    @IBAction func FS(sender: UIButton) {
        audioPlayerFS.play()
    }

    @IBAction func G(sender: UIButton) {
        audioPlayerG.play()
    }

    @IBAction func GS(sender: UIButton) {
        audioPlayerGS.play()
    }

    @IBAction func A(sender: UIButton) {
        audioPlayerA.play()
    }

    @IBAction func AS(sender: UIButton) {
        audioPlayerAS.play()
    }

    @IBAction func B(sender: UIButton) {
        audioPlayerB.play()
    }

    @IBAction func C4(sender: UIButton) {
        audioPlayerC4.play()
    }
}