The key to solving the problem is to find the running away suspect. 中to solving可否换成不定式？

不可以。

The key to solving the problem is to find the running away suspect.

解决问题的关键是找到逃跑的嫌疑人。

既然都说了to在这里是介词，后面加动名词，那么就不能和不定式混淆使用。

望采纳