Saw my first passport control yesterday

I saw my first passport control in Germany yesterday. I was in the Stuttgart train station waiting at the beginning of the platform for my train to arrive. About 20 feet away were a small group of people in civilian clothes who were hanging out, looking inconspicuously idle. A train on the adjoining tracks arrived and the passengers came streaming down the platform. One guy came down and stopped to look at the big electronic sign, detailing train departures. He was probably looking for his connecting train. He looked a little Middle Eastern, but could have been Italian, and had a small cloth shoulder bag.

In any case, as he paused to look at the sign he was surrounded by the small group of people who turned out to be cops. They asked for his passport, probably to see his domestic identification card which Germans have to have on them at all times. The cop who got his passport then left the group to make a call, probably to verify the info. The others asked him some questions and also took his bag and looked through it.

I would imagine if you were Turkish or Arab this could be a rather commonplace occurence. I don't know how frequent these controls take place, although that would be interesting to find out.