Robert Mueller said Wednesday that charging President Donald Trump with a crime was “not an option” under Department of Justice regulations.

WATCH: Robert Mueller makes 1st public statement on Russia probe

In his first public statement on the special counsel’s Russia investigation, Mueller said he followed two memos from the Justice Department’s Office of Legal Counsel that established a policy that a sitting president cannot be indicted or prosecuted because it would interfere with his ability to perform his constitutional duties.

Instead, Mueller said, “the constitution requires a process other than the criminal justice system to formally accuse a sitting president of wrongdoing.”

That points to impeachment, but Democrats have been divided on whether to begin impeachment proceedings against Trump, in part because of the political backlash they could face in the 2020 election.

Before Wednesday, Mueller had not spoken publicly about his investigation into Russian interference in the 2016 presidential election and potential ties to the Trump campaign. Mueller also said he was resigning from his position as special counsel.

Last month, the Department of Justice released a redacted version of Mueller’s final report.

In the report, Mueller concluded that there was no evidence of coordination between the Trump campaign and Russia. But he did not come to a conclusion on whether Trump committed obstruction of justice.

Mueller said Wednesday he would not speak further on the investigation, which appears to indicate he will not testify before Congress. He said the report he issued in April should “speak for itself.”

Two years ago, the Acting Attorney General asked me to serve as Special Counsel, and he created the Special Counsel’s Office.

The appointment order directed the office to investigate Russian interference in the 2016 presidential election. This included investigating any links or coordination between the Russian government and individuals associated with the Trump campaign.

I have not spoken publicly during our investigation. I am speaking today because our investigation is complete. The Attorney General has made the report on our investigation largely public. And we are formally closing the Special Counsel’s Office. As well, I am resigning from the Department of Justice and returning to private life.

I’ll make a few remarks about the results of our work. But beyond these few remarks, it is important that the office’s written work speak for itself.

Let me begin where the appointment order begins: and that is interference in the 2016 presidential election.

As alleged by the grand jury in an indictment, Russian intelligence officers who were part of the Russian military launched a concerted attack on our political system.

The indictment alleges that they used sophisticated cyber techniques to hack into computers and networks used by the Clinton campaign. They stole private information, and then released that information through fake online identities and through the organization WikiLeaks. The releases were designed and timed to interfere with our election and to damage a presidential candidate.

And at the same time, as the grand jury alleged in a separate indictment, a private Russian entity engaged in a social media operation where Russian citizens posed as Americans in order to interfere in the election.

These indictments contain allegations. And we are not commenting on the guilt or innocence of any specific defendant. Every defendant is presumed innocent unless and until proven guilty in court.

The indictments allege, and the other activities in our report describe, efforts to interfere in our political system. They needed to be investigated and understood. That is among the reasons why the Department of Justice established our office.

That is also a reason we investigated efforts to obstruct the investigation. The matters we investigated were of paramount importance. It was critical for us to obtain full and accurate information from every person we questioned. When a subject of an investigation obstructs that investigation or lies to investigators, it strikes at the core of the government’s effort to find the truth and hold wrongdoers accountable.

Let me say a word about the report. The report has two parts addressing the two main issues we were asked to investigate.

The first volume of the report details numerous efforts emanating from Russia to influence the election. This volume includes a discussion of the Trump campaign’s response to this activity, as well as our conclusion that there was insufficient evidence to charge a broader conspiracy.

And in the second volume, the report describes the results and analysis of our obstruction of justice investigation involving the President.

The order appointing me Special Counsel authorized us to investigate actions that could obstruct the investigation. We conducted that investigation and we kept the office of the Acting Attorney General apprised of the progress of our work.

As set forth in our report, after that investigation, if we had confidence that the President clearly did not commit a crime, we would have said that.

We did not, however, make a determination as to whether the President did commit a crime. The introduction to volume two of our report explains that decision.

It explains that under long-standing Department policy, a President cannot be charged with a federal crime while he is in office. That is unconstitutional. Even if the charge is kept under seal and hidden from public view—that too is prohibited.

The Special Counsel’s Office is part of the Department of Justice and, by regulation, it was bound by that Department policy. Charging the President with a crime was therefore not an option we could consider.

The Department’s written opinion explaining the policy against charging a President makes several important points that further informed our handling of the obstruction investigation. Those points are summarized in our report. And I will describe two of them:

First, the opinion explicitly permits the investigation of a sitting President because it is important to preserve evidence while memories are fresh and documents are available. Among other things, that evidence could be used if there were co-conspirators who could now be charged.

And second, the opinion says that the Constitution requires a process other than the criminal justice system to formally accuse a sitting President of wrongdoing.

And beyond Department policy, we were guided by principles of fairness. It would be unfair to potentially accuse somebody of a crime when there can be no court resolution of an actual charge.

So that was the Justice Department policy and those were the principles under which we operated. From them we concluded that we would not reach a determination – one way or the other – about whether the President committed a crime. That is the office’s final position and we will not comment on any other conclusions or hypotheticals about the President.

We conducted an independent criminal investigation and reported the results to the Attorney General—as required by Department regulations.

The Attorney General then concluded that it was appropriate to provide our report to Congress and the American people.

At one point in time I requested that certain portions of the report be released. The Attorney General preferred to make the entire report public all at once. We appreciate that the Attorney General made the report largely public. I do not question the Attorney General’s good faith in that decision.

I hope and expect this to be the only time that I will speak about this matter. I am making that decision myself—no one has told me whether I can or should testify or speak further about this matter.

There has been discussion about an appearance before Congress. Any testimony from this office would not go beyond our report. It contains our findings and analysis, and the reasons for the decisions we made. We chose those words carefully, and the work speaks for itself.

The report is my testimony. I would not provide information beyond that which is already public in any appearance before Congress.

In addition, access to our underlying work product is being decided in a process that does not involve our office.

So beyond what I have said here today and what is contained in our written work, I do not believe it is appropriate for me to speak further about the investigation or to comment on the actions of the Justice Department or Congress.

It is for that reason that I will not take questions here today.

Before I step away, I want to thank the attorneys, the FBI agents, the analysts, and the professional staff who helped us conduct this investigation in a fair and independent manner. These individuals, who spent nearly two years with the Special Counsel’s Office, were of the highest integrity.

I will close by reiterating the central allegation of our indictments—that there were multiple, systematic efforts to interfere in our election.

That allegation deserves the attention of every American.