The sentence in question: その理由を聞いてみると。
For full context: https://www3.nhk.or.jp/news/web_tokushu/2018_0521.html?utm_int=news_contents_tokushu_004
My attempt at translatino: "I tried to learn of the reasons."
The sentence itself seems fairly simple to me, however I have no clue what to do with this "trailing" と ^^
This と simply means "when". It's explained here. This is an "incomplete" sentence which is used to draw attention to the following part of the article. You can read this as if there were an ellipsis at the end of the sentence.
その理由を聞いてみると。
When we (the clue) asked the reason ...
We asked the reason, and ...
