A lonely secretive man is betrayed the first time he attempts being open. For the first time explicitly concerned with the consequences of his wire-tapping work, he mistakenly takes the wrong side in trying to avert these consequences. He is a passenger on a bus ride that he can neither control nor enjoy.
The picture seems more at ease with what it would not like to be rather than offering an alternative vision for art. If there is any suspense at all, it is in the anticipation of the resolution of the main character's mental state, not the crime that is about to be committed. The character is not interesting enough to merit such attention. As for the perpetrator and the victim of the brooding crime---and it is not apparent till the end who is who---neither is an honourable citizen inspiring sympathy.
The film tries to be realistic, which is ambitious as realism usually betrays the lack of imagination and artistic talent. Interesting people are almost never "realistic." Neither are films. The film is a concept in search of a better execution. "Das Leben der Anderen" (2006) is the better execution.