Robert Morgenthau in his office at Wachtell, Lipton, Rosen & Katz in 2013. Photo: Rick Kopstein

For generations of prosecutors, Robert Morgenthau was “The Boss.” The three of us served as heads of the District Attorney's international bureau, known informally as DANY Overseas. Even after he retired 10 years ago, he remained a strong presence in our lives, calling to discuss his latest cause—assisting immigrants, getting someone off death row or helping support his kids at the Police Athletic League or fighting anti-Semitism and neo-Nazi activity as chair of the Museum of Jewish Heritage. He had slowed down a bit; his hearing wasn't great; but his mind was sharp; his passion for justice was great; and he well remembered who had stood up and who had not, over many decades. We and the thousands of others who had learned their craft and their ethics from the Boss were certain we would be celebrating his centenary and can hardly believe he is gone, mere days before his 100th birthday.

He knew everyone, but no one ever got a break on a case that they did not deserve on the merits. Mr. Morgenthau kept everyone honest. He believed and repeated that “you cannot prosecute crime in the streets without prosecuting crime in the suites.” In a democracy, he believed, that is critical.

When the international bureau was started, we were the first and no one could understand how or why a local prosecutor was prosecuting the largest international frauds in the world. He knew what Manhattan's financial markets meant to the world—more than knew it, he intuited it. He would always say that we were the local beat cop for global financial markets. When federal prosecutors failed to be sufficiently aggressive against the big banks or foreign leaders whom the State Department did not want to be the subject of legal scrutiny, Mr. Morgenthau kept everyone honest.

The obituaries have been many, but we wanted to share our personal memories of the Boss and his influence on our careers and our characters. Running DANY Overseas was probably the highpoint of our professional careers. It was a bureau that Mr. Morgenthau created, and the bureau chief effectively reported directly to him. He'd call one of us and ask if we had any time to spare to come see him. As if he was intruding on our time. He would have read something in the papers about finance or international business that troubled him, and he'd call us in to brainstorm. “What can we do about this?” he would ask.

In the early 1990s we were referred a case by Sen. John Kerry's counsel involving the Bank of Credit & Commerce International—BCCI. The Bank, supposedly a $23 billion institution with offices in 80 countries, had exceedingly cozy relations with members of government around the globe, who were able to quash investigations when anyone started to look at it seriously. Foreign governments complained about the investigation but Morgenthau was willing to go where the evidence led. For him it was the only way to go. The bank was revealed as a Ponzi scheme and a factory for laundering money. It was shut down.

Later on, we were chasing dirty money from South America to the Middle East, and Mr. Morgenthau was increasingly focused on Hezbollah activities in South America and Iran's ability to evade sanctions. We started working with foreign prosecutors and intelligence services who would give us detailed information simply on the strength of the Boss's name and reputation. We would show up to work on Monday and the Boss would tell us we were flying to Israel the next day. Or Paraguay. Or Brazil. In an office where business travel usually meant a subway ride to Washington Heights, this was exciting stuff.

Thanks to his focus and determination, we got into some important international cases: the Alavi Foundation, WMD proliferation, indicting the Iranian shipping line, and finally cases where banks were stripping transaction information showing Iranian involvement. One of the last big cases of his career was the settlement with Credit Suisse late in 2009. Credit Suisse had been trying to delay the case until after the Boss left. Our team worked around the clock and two weeks before Mr. Morgenthau's retirement, we reached a significant settlement. We sat down in front of his desk and waited for some words of praise, job well done, perhaps some reminiscing. He raised an eyebrow and asked if we could get any more cases done before the end of the year.

He believed that justice knew no race, creed, color or income bracket. He took on cases that were novel if they were important and he believed in them, even if there was a risk they would be lost. He was a great man, and a good man. He inspired us and so many others to do great things. We will miss him.

Adam Kaufmann, Art Middlemiss and John Moscow work together at Lewis Baach Kaufmann Middlemiss, a law firm in New York City and Washington, D.C.