Would this marriage be valid?

The man is an unbaptized pagan, and he marries a non-Catholic (possibly baptized, but uncertain) divorcee in either a civil or non-denominational ceremony at some facility in the mountains.

Do we first need to know the status of her first marriage before concluding anything about the new marriage?  If this information cannot be ascertained, do we just give the benefit of the doubt and presume validity until someone else presents information proving the contrary (or does the previous divorce remove the presumption of validity)?