find out 用作及物或不及物动词均可：用作及物动词的意思是“发现（真相）”，用作不及物动词的意思是“发现真相”，你的句子中 As far as I have been able to find out 的意思“根据我所发现的事实真相”，即“据我所知”，你的句子意思是：

As far as I have been able to find out, he has no criminal convictions. 据我所知，他没有被判过罪。

更多例句如：

As you will find out, I will never let you down. 你将会发现，我绝不会让你失望。

So far as I can find out, the figures have been greatly underestimated. 据我所知，这些数字大大地低估了。

If the newspapers find out, he’s finished in politics. 如果报界发现这些问题，他的政治生涯就完了。