In a nutshell, a civil investigation uncovers and documents evidence necessary for a civil trial. Civil court, as opposed to a criminal trial, generally involves two opposing parties who disagree on some matter or issue that affects them.
For example, one party may have been injured in an automobile accident and does not agree with the amount the other party (or their insurance) is offering for damages stemming from the accident. In that situation, the injured party might decide that a civil trial is necessary to resolve their differences.
There are always two sides to a civil trial. Whether you are the plaintiff or the defendant the information obtained through a civil investigation is essential to prevailing at such a trial. Please keep in mind, that in a civil trial, the judge or jury need only believe one party over the other (51% to 49%) for the believed party to prevail – that’s called the “preponderance of the evidence.”
There are a nearly infinite number of situations where a “civil” investigation might be needed. In this context, “civil” is meant to encompass all situations that are not specific violations of criminal law, and thus, not considered “criminal” on face value.