Also known as "based on a true story". To fictionalize a story is to take something that really happened and make it purely a story: Leave out or replace details, such as names and other personal information.
Such fictionalization has two advantages. One is that it protects the integrity of those involved in the actual case. The other is to get to focus on the topics expressed through the story, without any distractions about "Is this truly what happened? What about the other point of view?" and so on.
Such distractions are highly relevant when an actual case is being discussed: While a story may or may not be a reasonably fair depiction of actual events, It is always told from a point of view. It is thus never a completely impartial objective truth.
The opposite of fictionalization is the narrativism of taking a story and claim it to be the one and only relevant objective truth that everyone must believe in.