I've seen two different examples in the news recently where police in the US or UK were looking for somebody and suspected they had left the country... but could not be certain - presumably there was no record or evidence of them leaving. One was a missing person's case in Wisconsin, US where someone faked their death and fled to Eastern Europe, the other was a murder in the UK where the prime suspect is thought to have fled the UK.

In both cases the people were not well connected criminals but relatively ordinary people which would seemingly rule out smugglers or fake passports.

How is it possible these people left the country? Surely if they went through any official venue like an airport or boat their passports would have been scanned and this would have been logged somewhere the police could have retrieved it?

Even if the US guy somehow got across a blindspot in the border to Mexico or Canada, how is he going to get to Eastern Europe from there?