Arun Rao, the federal prosecutor in charge of overseeing cases for the division that covers Prince George’s and Montgomery counties for the past two years, has left for a position in the private sector.

Rao starts Monday as executive vice president of Investigative Group International and its affiliated law practice, the Lenzner Firm, based in Washington, D.C.

Rao, who also worked at the White House during the Obama administration, will lead “corporate internal investigations, advising clients on risk management, white-collar prosecutions and government investigations,” according to an announcement from the firm.

As chief of the Southern Division of the U.S. attorney’s office for the District of Maryland under Rod J. Rosenstein, who is now Deputy Attorney General, Rao managed a wide range of high-profile cases involving public corruption, gang activity, terrorism and money laundering.

Rao, 41, who lives on Capitol Hill with his wife, reflected on his time as a federal prosector in an interview with The Washington Post last week. This has been edited for length and clarity.

Arun Rao, former chief of the Southern Division of the U.S. attorney's office for the District of Maryland. (White House)

What are some cases you’re proud of during your time in the U.S. attorney’s office?

The office has done some remarkable cases over the past six months. We have had MS-13 prosecutions that have just been terrific. Those assistant U.S. attorneys put their heart and soul into these cases. Through grunt work and work with cooperating witnesses, they’ve been able to secure a number of verdicts in the past few months where defendants have received life in prison.

One case I played a part in firsthand was among public corruption cases we called "Operation Dry Saloon." [The case involved liquor store owners bribing lawmakers in exchange for favorable votes on legislation that would expand liquor sales in Prince George's County.]

That’s just been a real success as far as what you want to see out of a public corruption investigation. The legislature introduced and the governor signed the public integrity act in response to our investigation.

It’s a source of pride for us at the U.S. attorney’s office when we can see the work we do have a tangible impact in the world.

United States v. Waffen was a case I handled in 2011 and 2012 involving the largest theft ever from the National Archives, which was perpetrated by a former supervisory archivist. The theft of our nation's history by someone who was entrusted with its preservation was unconscionable, and I am proud of my work in that case.

What are some trends you’ve noticed in your time as a federal prosecutor?

The opioid crisis is one of the greatest and most rapidly increasing public health and criminal justice problems facing Maryland. In 2012, Deborah Johnston and I successfully tried the first case involving the distribution of heroin resulting in death in federal court in Maryland: United States v. Sweeney. The defendant was sentenced to 20 years in prison, the mandatory minimum sentence under federal law.

Since 2012, sadly, the prosecution of these types of cases by our office has become far more common — and now frequently involve dangerous substances like acetyl fentanyl and carfentanil. Earlier this year, prosecutors in the Greenbelt office secured a sentence of life in prison in a case involving the distribution of acetyl fentanyl resulting in death. And earlier this month, I spoke at the Maryland State's Attorneys' Association board meeting about the ability of federal prosecutors to help state prosecutors with this growing problem, which threatens to overwhelm local authorities. I expect that as U.S. attorney, Rob Hur will continue to devote substantial resources to this area.

The MS-13 cases definitely seem to be more prevalent than when I began. What I have noticed over the past couple of years is that the geography within which these guys are operating is expanding. It used to be just in Langley Park. Now it’s in Montgomery County and eastern Virginia, and now we have a case where some members are involved as far south as rural Virginia, and we’re doing cases in Frederick. Regionally, not withstanding our best efforts, we’re still seeing a spread of the violence. The most puzzling and alarming thing in the MS-13 cases is the violence seems almost purposeless. It is violence for violence’s sake.

You’re leaving the U.S. attorney’s office in Maryland at a time of transition. Well-respected longtime federal prosecutor Deborah Johnston recently died, and Robert K. Hur is expected to take over the office after Rosenstein left.

Deborah Johnston was just a legend. She was the finest attorney I’ve worked with and an even better person. Sometimes I feel like I’m leaving the office at a difficult time for folks I consider friends and colleagues. I take comfort in the fact that the office is in good hands. Rob and I handled cases together in the past. He’s someone with integrity, intelligence and humility. I’m confident he’s going to maintain the high standards of the office. The office in Greenbelt is going to be in good hands with Kristi O’Malley, who will be handling things until Rob is confirmed.