German managers view themselves more as mediator than judge. Mediation in Germany means gathering and analyzing the facts only. Subjective input, the viewpoint of others affected by the dispute, carry far less weight.
An American manager sees himself more as judge than mediator. Both facts and subjective information are considered in his deliberations. "Witnesses" will be interviewed.
The American approach is too susceptible to manipulation. Colleagues often choose sides in a conflict. Their testimony is inherently subjective.
Many conflicts are the result of non-quantifiable, nuanced, context-oriented factors. There is a fine line between objective and subjective information. The German approach takes into consideration only the factual evidence.
Advice to Germans
Go beyond the literal, quantifiable facts. Talk to the folks close to/or impacted by the internal conflict. An American party to the conflict will ask and expect you to get their colleagues' opinion on the conflict.
To ignore that input as subjective, is to not gather all of the facts. If your team leader is an American, anticipate him/her talking to all sorts of folks in the organization in order to get as complete a picture as possible. Line up your references.
Advice to Americans
If you lead Germans, go ahead and interview folks near and impacted by the conflict. But be sure to start with the facts. Otherwise, your approach could be misperceived as relying too much or exclusively on hearsay.
If your German boss is involved, avoid suggesting that he/she talk to folks who support your point of view. That could be perceived as attempting undue influence on the process.