Homicide Detective J. Warner Wallace tells of a time when he arrived at a crime scene after the regular police had already responded. It was raining hard, and the police officer who was first on the scene had rounded up the witnesses and put them in the back of the police car to keep them out of the rain. In so-doing, the officer had unwittingly damaged the eyewitness testimony. When Wallace interviewed the witnesses, all of their stories sounded the same. Why? Because when they were together in the car, they had talked to one another and their stories synced up.
In order to investigate the crime, Wallace was counting on each eyewitness telling the story from their point of view. By looking at the differences in the stories, Wallace would have been able to gain a better idea of what had actually happened. When the stories synced, they had lost their nuance and damaged the case.
If the Gospels are eyewitness testimonies, one would expect the same kinds of nuance that is true of other kinds of eyewitness testimony. And in fact, this is exactly what we find.
In his book, Undesigned Scriptural Coincidences, scholar J.J. Blunt lists an enormous number of events recorded in scripture that unintentionally support one another, just as one would expect from several eyewitnesses reporting the same event. Here are a few examples: