THE LIVES OF OTHERS (Das Leben Der Anderen 2007)

The story is set in Communist East Germany (GDR) around 1984, and the main character isa Stasi officer, Gerd Wiesler (Ulrich Mühe) operating under the secret code HGW XX/7.
He is a veteran in the Stasi whose specialty is interrogations and one way or another, he is able to get  information he needs from those he is questioning.

One night his boss takes Wiesler to the theatre and suggests he take an interest in a potentially dissident playwright, Georg Dreyman (Sebastian Koch), whose beautiful girlfriend (Martina Gedeck) is appearing in his new play. 
Once the playwright's apartment is wired, Wiesler and an assistant start 24/7 surveillance  from the apartment above.

The film turns into a suspenseful thriller with a complex and powerful moral drive, and  in the process Wiesler himself gets transformed (The scene in elevator with neighboring kid powerfully showcases that change) .

At the end of film Wiesler , working as postman,  years after the original events took place ,two years after the fall of Berlin Wall and GDR dissolution , spots the book in the store window, titled Sonate vom Guten Menschen (Sonata for a Good Man), and immediately recognizes the author's picture.
He goes inside and opens a copy of the book and reads the dedication "To HGW XX/7, in gratitude". 

This brilliant film won the best foreign language film at the 2007 Oscars, and has been regarded by some as the best-ever German film.

"He sits like a man taking a hearing test, big headphones clamped over his ears, his body and face frozen, listening for a faraway sound. His name is Gerd Wiesler, and he is a captain in the Stasi, the notorious secret police of East Germany. The year is, appropriately, 1984, and he is Big Brother, watching. He sits in an attic day after day, night after night, spying on the people in the flat below.
Wiesler is a fascinating character. His face is a mask, trained by his life to reflect no emotion. Sometimes not even his eyes move. As played in Muehe's performance of infinite subtlety, he watches Dreyman as a cat awaits a mouse. And he begins to internalize their lives -- easy, because he has no life of his own, no lover, no hobby, no distraction from his single-minded job.