In my areas of legal practice, personal injury and criminal defense, the early investigation is critically important. It is part of the lawyer's job to coordinate and direct the investigation.
In personal injury cases, the first hurdle is to establish liability. What did the defendant do that was negligent? In accident cases, any eyewitnesses should be interviewed in detail as early as possible. A good investigator will either make a recording of the statements or thoroughly document witness statements in a report.
In slip and fall cases, it is usually necessary to establish: (1) that there was a dangerous condition on the defendant's property and (2) that the defendant knew or should have known of the dangerous condition.
Eye witnesses may establish that the dangerous condition had been present for some time and the defendant or his employees should have noticed and remedied the danger or at least warned people of the danger.
The defendant and defendant's employees can also be interviewed. They may admit to the dangerous condition and explain that they planned to resolve the problem but didn't get around to it. An admission like this will probably result in an excellent result for an injured plaintiff!
In auto accident cases, the same recommendations apply even if the police investigator blames the defendant driver for the accident. The defense may argue that the plaintiff was partly at fault for the accident and they likely will have their own accident reconstruction expert to back up their position. If this happens, your early investigation may save the day.
It is always essential to interview the defendant driver to obtain his or her version of how the accident occurred. If the defendant driver admits fault, plaintiff's attorney can move on to establish the damages (medical bills, pain, and suffering, loss of earnings etc.).
Your investigator should ask the defendant driver about his insurance policies and their limits. The defendant's insurance limits and assets may affect the strategy for the handling of the case.
Finally, in every personal injury case, photographs or video of the location of the accident, vehicles involved and the plaintiff's injuries should be taken by the plaintiff's investigator.