How to detect Delete key press in Swift?

NSEvent.addLocalMonitorForEvents(matching: .keyDown) {
    if self.keyDown(with: $0) {
        return nil // needed to get rid of purr sound
    } else {
        return $0
    }
}

private func keyDown(with event: NSEvent) -> Bool {
    if event.charactersIgnoringModifiers == String(UnicodeScalar(NSDeleteCharacter)!) {
    	print("Delete key presses!")
        return true
    } else {
    	return false
    }
}