Sich (bei etwas) um etwas handeln is a German idiom corresponding to be a matter of. The grammatical structure is slightly different, but these examples should help:
- Es handelt sich um Mord. It is a matter of murder.
- Bei diesem Fall handelt es sich um Mord. This case is a matter of murder.
The German idiom is clearly related to one found in Romance languages that is used in much the same way, but with the bei … part optionally added when more information should be provided. (I am not sure, but the optional part may only exist in German. I think in French one would have to resort to “En ce qui concerne ce cas …” or “Quant à ce cas …”)
- Il s’agit de meurtre.
- Se trata de un omicidio.
- Se trata de un asesinato.