Five observations about the first indictment reportedly returned by the grand jury empaneled by Special Counsel Robert Mueller to investigate links between the Trump campaign and Russian interference with the 2016 election:

First, an indictment means that a grand jury has found that probable cause exists to believe that a crime has been committed by a particular defendant or defendants. Probable cause means a reasonable basis or fair probability that a crime has been committed, a lower standard of proof than the guilt beyond a reasonable doubt required for conviction at trial. But Department of Justice policy provides that a prosecutor should file charges only if there is a reasonable likelihood of conviction at trial, where the standard of proof is guilt beyond a reasonable doubt. Because Mueller is required to comply with DOJ policy, an indictment means that he and his team believe that they have evidence sufficient to meet this higher standard.

Second, this is likely only the first of several indictments.

One extreme scenario is that the sealed indictment charges President Trump himself. It is possible that Mueller has had sufficient time to complete his investigation of obstruction of justice against the President. The obstruction case would involve a somewhat isolated series of events that are less complex than the larger interference investigation. Reports indicate that Mueller has been investigating Trump’s request to former FBI Director James Comey to end the investigation into former National Security Advisor Michael Flynn and related acts that could amount to obstruction of justice. While the law is unclear, under DOJ policy, a sitting president cannot be held to answer to criminal charges in court and may only be impeached. One way to handle that scenario is to indict him now, seal the indictment, and unseal it on the day he leaves office by impeachment or otherwise. In light of the complexities and importance of the case, however, it seems unlikely that Mueller has reached this point yet.

The more likely scenario is that they have charged one or more lower-level individuals, such as Flynn, former campaign chairman Paul Manafort, or maybe even someone whose name has not been reported publicly. One potential charge is violation of the Foreign Agent Registration Act, which requires individuals who work as agents of foreign governments to provide notice of that fact to the Attorney General of the United States. Both Flynn and Manafort ultimately filed such registrations, but only after substantial delay and public exposure of the work they had already done on behalf of foreign governments. Regardless of what crime has been charged, as the investigation goes on, it could be that additional charges against this defendant or other defendants will be added in superseding indictments or separate indictments.

Third, the defendant or defendants charged in this indictment are likely to be those that the Mueller team will try to “flip.” Flipping witnesses, a common tactic that prosecutors use, means persuading lower-level defendants to cooperate as witnesses against more culpable defendants in exchange a recommendation of leniency. If Mueller is employing this strategy, this indictment may include charges against someone close to the Trump campaign who has information that could be of value to Mueller and his team. Manafort, for example, was reportedly a key participant in the June 2016 meeting between Russians, Donald Trump, Jr., and Jared Kushner to obtain disparaging information about Hillary Clinton. If Manafort were to cooperate, he could potentially provide important details about what Trump Jr. and Kushner said and did regarding that meeting. There have been reports that Manafort has already been told that he would be indicted. Some have portrayed that notice as a scare tactic. To the contrary, it is not uncommon to warn a target that he will be indicted to give him an opportunity to cooperate before the indictment is filed. A defendant who refuses to cooperate at that stage of an investigation may have a different perspective once he has been charged with a crime.

Fourth, reports also say that the indictment was ordered sealed by a federal judge. Sealing an indictment for a short period of time is a common practice. Obtaining a sealing order requires a showing by the prosecutors that there is a legal basis, though it is routinely granted. One such reason is to avoid alerting the defendant to the existence of an indictment and providing a chance for him to flee or destroy evidence before he can be arrested. Another reason is to prevent co-conspirators from learning about the indictment and changing their behavior in some way that jeopardizes the investigation, such as by tampering with witnesses or evidence or even coordinating their explanations. Here, it could be that the prosecutors simply want to obtain a bit of time to organize an arrest plan for early next week or to provide notice to lawyers for the defendants so that they may voluntarily surrender at a reasonable time. On the other hand, it could be that the indictment (or others not yet reported on) will remain sealed for a longer period of time while the investigation continues, so as not to tip off witnesses and co-conspirators regarding where the investigation is heading until it is complete.

Finally, Mueller is living up to his reputation for working with urgency. In a case of this complexity, with potential witnesses and evidence located all over the world, a thorough investigation could take many months or even years. Mueller appears to have returned his first indictment about five months after his appointment. Why might an investigation take such a long time? In all cases, investigators first want to get their arms around all of the documents and tangible evidence, and then interview witnesses so that they can ask them informed questions. In this case, that task likely involves thousands of emails, memos, letters, and financial records, including some from foreign banks. In addition, some reports have stated that the Foreign Intelligence Surveillance Court authorized surveillance of two Trump associates, Manafort and former campaign advisor Carter Page. There are also indications that Flynn and then Senator and now Attorney General Jeff Sessions were intercepted speaking to the Russian ambassador during the campaign. If true, Mueller and his team would need to sift through all of those recordings to identify any relevant evidence.

Only after this enormous task is accomplished can witnesses be interviewed. In most cases, some witness interviews prove fruitful and others do not. The fruitful witnesses may then need to testify before the grand jury. Often, witnesses identify other people with knowledge of the subject matter, creating the need to conduct additional witness interviews. Only after all of these potential sources of information are exhausted as to a particular charge is a prosecutor ready to ask a grand jury to return an indictment. With 16 top prosecutors on his team, Mueller appears to have reached this point, at least as to part of the case. I have no doubt that he has had his team working long days, nights, and weekends to complete their work.

And there is likely more to come.