Paul Callan is a CNN legal analyst, a former New York homicide prosecutor and currently is counsel at the New York law firm of Edelman & Edelman PC, focusing on wrongful conviction and civil rights cases. Follow him on Twitter @paulcallan . The opinions expressed in this commentary are his own.

(CNN) The unsealing Monday of the first indictments arising from Robert Mueller's investigation provides many valuable hints regarding the future direction of the special counsel's probe.

The use of sealed indictments and Mueller's decision to do an 11-year look back into former Trump campaign chairman Paul Manafort's prior business operations will make President Trump's personal lawyers very nervous today. Will the special counsel do a similar look back to 2006 on any aspects of the Trump business empire now that the Manafort indictment has opened the door?

As CNN reported Monday , Manafort and former Trump campaign official Rick Gates have turned themselves in to Mueller, who unsealed an indictment against them on 12 counts, including conspiracy against the US, conspiracy to launder money, being an unregistered agent of a foreign principal, and making false statements.

The criminal justice system is presumptively open to public view. The only exceptions to this rule apply to grand jury proceedings and occasional matters relating to such things as national security, confidential informants or threatened witnesses. This transparency, required by the US Constitution, is obviously even more important in a free society when a criminal investigation focuses on the sitting president's election campaign and claims of "collusion" and possible tampering by a hostile foreign power.

So why the sealed indictment in a case that cries out for full disclosure? Such indictments are generally used when there is a fear that a criminal suspect, with knowledge of a pending indictment, might flee the jurisdiction, destroy evidence or even threaten witnesses likely to testify against him at trial.

In cases involving organized crime, drug dealers and crimes of violence, sealed indictments are a sensible way to make sure the suspect doesn't escape and that witnesses are not harmed. For instance, the infamous Joaquin "El Chapo" Guzmán, alleged leader of Mexico's Sinaloa drug cartel who is now awaiting trial in a Brooklyn federal jail, was indicted via a sealed indictment.

In so-called "white collar" investigations like the Mueller probe, the sealing and delayed disclosure of the indictment is sometimes done, not out of prosecutorial fear, but as a courtesy to a prospective defendant who has been generally cooperative. This enables the suspect's attorney to arrange a quiet, voluntary surrender of his client without one of those embarrassing handcuffed "perp walks" often staged by then-US Attorney Rudolph Giuliani in the 1980s and by other publicity-seeking prosecutors.

The high-profile nature of the potential targets in the Mueller investigation make it unlikely that they could successfully flee the United States to avoid prosecution. Of course this cannot be entirely ruled out, because so much of the probe focuses on the relationship Trump campaign officials allegedly maintained with Russia, a hostile power which has sheltered American fugitives such as Edward Snowden.

Sending a message

Early indictments in high-profile investigations often "send a message" to other potential suspects that anyone who seeks to obstruct the investigation may face indictment regardless of who they are or who they know.

Of course, prosecutors will deny indicting someone just to "send a message," but even an entirely legitimate indictment based on strong evidence can have this collateral effect. Even ethical prosecutors would say that there is nothing wrong with allowing a perfectly proper indictment to serve a dual purpose.

The type of charges that would send a message include lying to the FBI or other federal investigators. Anyone who tells such a lie can be charged with a felony, as can anyone who testifies falsely about a material fact before Congress.

Charges relating to obstruction of justice can also be lodged in situations even where the original suspected crime cannot be proven. The old saying that "it's not the crime but the coverup" that you must worry about is quite true. This message can be sent with frightening clarity to all potential White House witnesses through early "message sending" indictments.

Sometimes tough prosecutors pick on surprising targets to inflict pain and induce cooperation from resistant suspects. They go after family and close associates. Since Mueller is following the tax and money-laundering road, he can really exert pressure with a threat to arrest a wife or other family members who may have been involved in the suspect's business and/or signed off on tax returns.

The arrest of a wife or child is a strong inducement to get cooperation from a stubborn and resistant "target." And yes, such indictments and arrests really do happen in high-profile tax and money laundering cases.

Make no mistake, the widely praised Mueller is no softie and is capable of such a maneuver. We already know that Mueller's team executed a "No Knock" warrant permitting a pre-dawn raid at Manafort's home. Raiding agents seeking financial records reportedly also rummaged through closets looking at clothing and other items there. It is obvious in hindsight that they were exploring the subject of money laundering or even possible tax charges in seeking such records and making visual observations to see if the Manafort lifestyle was commensurate with his reported income. A similar approach was used to get Al Capone.

Paul Manafort has continually maintained that he is innocent of any wrongdoing.

Mueller may have had to move quickly in bringing charges against Manafort because the six-year statute of limitations for tax fraud may be expiring. This statute of limitations could have been a key determining factor in selecting early indictment targets.

A chill?

Such charges based on business operations and tax returns filed prior to the Trump campaign but "arising from" the election tampering investigation are perfectly legal under Mueller's charge from Deputy Attorney General Rod Rosenstein.

Yet a look back at pre-campaign business operations would be likely to send a chill through the White House. This would suggest that an examination of Trump's pre-campaign business operations is now a real possibility, crossing the previous "red line" described by the President.

Trump's Achilles heel may well be found in the pre-campaign operation of the complex and varied transactions of his business empire rather than in an explicit conspiracy with the Russians to tamper with the American election.

The president will not find solace or refuge in the pardon power of the presidency should the Mueller probe zero in on him by "flipping" witnesses with early indictments. In fact, pardons will backfire since a pardoned suspect can no longer avoid testifying by asserting the 5th Amendment's protection against self-incrimination.

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Once pardoned, the witness faces no criminal exposure for his underlying crimes and can be forced to testify. And the Fifth Amendment cannot be used as a shield against perjury charges as a pardon, when bestowed, cannot apply to future crimes.

Given the serious developments today, the President is likely to adopt a new policy: vetting his tweets about the Mueller Investigation with his personal counsel.