Task::deleteDocument

static function deleteDocument($documentId)
{
	$res = CTasks::GetList([], ['ID' => (int) $documentId, 'CHECK_PERMISSIONS' => 'N'], ['CREATED_BY']);
	if ($res && ($task = $res->Fetch()))
	{
		$prevOccurAsUserId = BitrixTasksUtilUser::getOccurAsId(); // null or positive integer
		BitrixTasksUtilUser::setOccurAsId($task['CREATED_BY']);

		$task = new CTasks();
		$task->delete($documentId);

		BitrixTasksUtilUser::setOccurAsId($prevOccurAsUserId);
	}

	return true;
}