That is a shame but might i suggest you put brand new people in a rank with no chest access, give them a set amount of time of your choosing and then promote them to a higher rank call them "fresh meat" or something (obviously don't use something that cliche, but you get my point) it will help prevent that from happening again and give you some time to know the person.

I suggest this to any FC honestly, who don't background check members (asking if anyone knows them or of them)