A German manager who has been asked to resolve a conflict is more mediator than judge. And mediation in Germany means gathering and analyzing the facts only. Subjective input provided by others affected by the dispute, carry far less weight.
An American manager asked to resolve a conflicts sees himself more as judge than mediator. Both facts and witness testimony will be considered in her deliberations. Both are legitimate forms of evidence.
From the German point of view the American approach is too susceptible to manipulation. Colleagues often choose sides in a conflict. Their testimony is inherently subjective. Justice means sticking to the facts only.
Many conflicts are the result of non-quantifiable, nuanced, context-oriented factors. Often there is a fine line between objective and subjective evidence. The German approach takes into consideration only the factual evidence. That is insufficient.
Advice to Germans
Go beyond the literal, quantifiable facts. Talk to the folks near to or impacted by the internal conflict. An American party to the conflict will ask and expect you to get the opinion of colleagues who see the situation as they do. To ignore that input as subjective, is to not gather all of the facts.
If your team lead is an American, anticipate her talking to all sorts of people in the organization in order to get as complete a picture as possible. You need to line up your references.
Advice to Americans
If you lead Germans go ahead and interview colleagues 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 she talk to folks who support your point of view. That could be perceived as attempting to unfairly influence the process. It could work against you.