The two 了 in the sentence indicate the same meaning. Normally when we use 了, we want to express the meaning that we did something (a past tense). In your example, 找到了 means "found the police", 还了钱 means "returned the money".

I think your issue is not actually the 了 here. I think you are reading 還 as hai2. Here, 還 is pronounced huan2, and it means to return money. 了 indicated that the action has happened. The old man found the police, and returned the money to him (I presume this means the police returned the money to the old man).