The official database.

If someone has a criminal record for criminal cases brought for administrative violations - this could know only a law enforcement officer. Of course, in the underpass, you can buy any base, but where is the guarantee that written there is true? And even if we assume that a number of us under a false passport goes criminal who listed in the criminal investigation, as to get his fingerprints? Wouldn't that be dangerous? It's every home-grown Sherlock Holmes must decide for himself.
Outdoor legal Internet search. Every day he writes a dossier. But in order to gather information, you need to use different search engines, think about various combinations of key words, to check all the available social networks and virtual Dating services. You can search not only by name but by email address or username of an online Communicator. If the name is unique enough and sociable person, then you are lucky. Of course, it is important not to confuse people with similar names or online nicknames.
Circle. Man is what surrounds it. Consequently, his friends, relatives is a part of his past. Intimate conversation helps to get to the true causes of behavior. But first you need to see them in person: to pay attention to unusual habits, fears, unjustified aggression on the occasion of any phenomenon or issue. Aggression, perhaps, is the first and most important bell about the mental state of a person. And there is no pressure on him what he can't admit it?
Analyst. The past is very difficult to eradicate. If the person has long been in a homogeneous cultural environment (for example, was an athlete, musician, military, or even spent time in places not so remote, its vocabulary, habits can echo many, many years. You need to pay attention to unusual words, scars, tattoos, style of dress. And match.
Irrational methods. The most intuitive, perhaps, is physiognomy. Masters of this art believe that a person's past imprinted on his face. For example, the horizontal lines characteristic of the powerful man, the Manager. Palmists and astrologers also claim this ability. But the first and the second see, at best, only a "bouquet of senses", but not the events themselves. And clairvoyants - people are so diverse that you can trust one hundred percent to the first comer psychic fraught.
A Frank conversation. Sincerity and trust - the key to a healthy relationship. We want to know a person's past not only to protect themselves but also to manage it. And our second half is not always hiding something criminal. Silence helps to distance himself from a certain painful issue, which is irrelevant to this, but it wounds the heart of the most taciturn. And if to reopen the wound, that loving people will not be able to build a future, live in present and be like two passengers jammed the carousel, constantly return to the past.