def filter_for_initial_manifest(objects, manifest):
    """
    Find the initial manifest created at the beginning of a export request.

    :type objects: list
    :param objects: List of objects in a particular bucket.

    :type manifest: str
    :param manifest: The expected identifier for the initial manifest.

    :rtype: str
    :return: The identifier for the initial manifest object.

    :raises RuntimeError: If the initial manifest is not found.
    """
    for obj in objects:
        key = obj['Key'].casefold()
        if key == manifest.casefold():
            return key
    raise RuntimeError('Initial manifest not found.')