True crime writers take a murder case and explore it from beginning to end, going into great detail about the partipants, their actions, and their motivations. It takes a mountain of research to make sure all the facts are correct. Otherwise, they would likely face a lawsuit. Some do anyway.
Mystery fiction writers take an actual case and change enough of the facts that they can say whatever they wish without getting into trouble. That's what I did in my first Greg McKenzie novel.
I wanted to saddle Greg with a recent troubled past. I had him quickly tire of retirement and take a job as an investigator for the district attorney in Nashville. I needed something that would get him fired from his job, plus anger many in the police department. I picked a case that remained unsolved but was in and out of the news on a regular basis.
A young lawyer had reported his wife, a talented artist, missing two weeks after she supposedly left home for a "12-day vacation" following an argument. Her friends said she would never leave her young son and daughter like that. The police quickly targeted the husband but were unable to find a body.
I changed the husband to a CPA and the wife to an interior designer. They had only a young son. But I kept most of the circumstances of the police search and their concentration on the husband as the murderer.
In the real case, the wife was the daughter of a prominent local attorney, who sided with the police in believing his son-in-law guilty. I made the missing wife the daughter of a prominent banker, who was the chief backer of the district attorney. When my protag, Greg McKenzie, makes some off-the-cuff remarks quite critical of the lead investigator, they turn up on the front page of the newspaper. The wife's father is infuriated and Greg gets fired.
Long after my book was published, the actual case reached a conclusion when the husband's father turned on him and testified he had helped dispose of the wife's body. The story was told in a true crime book titled An Unfinished Canvas, by Nashville author Phyllis Gobbell and Michael Glasgow.
Fictionalizing fact is a much simpler operation. Of course, Nashvillians who read my book recognized the similarity to the Janet and Perry March case. After his conviction in August of 2006, March was sentenced to 56 years in prison. I can't tell you what happened to the young CPA in Secret of the Scroll. That would be a spoiler.