WASHINGTON — The special counsel investigating former president Donald Trump’s alleged mishandling of classified documents and the Jan. 6 insurrection honed his investigative and trial skills over 30 years of fighting cases involving corruption, crimes and police brutality.

John L. “Jack” Smith was part of a team that won the first death penalty case in a New York federal court in a half a century, then went on to the International Criminal Court, where he prosecuted genocide and war crimes. As a federal prosecutor in Brooklyn, New York, he handled some of the city’s most violent cases, former colleagues say.

Jack Smith, the Department of Justice’s chief of the Public Integrity Section, poses for a photo at the Department of Justice in Washington on Aug. 24, 2010. Charles Dharapak/Associated Press file

Smith’s next assignment is overseeing the probes into former President Donald Trump, one of the most challenging and significant Justice Department investigations in years. People who have worked with Smith throughout his career describe him as determined, impartial and up to the task.

“Jack’s a prosecutor’s prosecutor,” said Morris Fodeman, Smith’s former colleague and now a partner at Wilson Sonsini Goodrich & Rosati PC. “He’s one of the best I’ve ever witnessed, an apolitical person who’ll call it the way he sees it.”

Fodeman teamed up with Smith in 2007, when he won the conviction of Ronell Wilson for the execution-style killing of two undercover NYPD detectives in 2003, the first time a federal jury had voted to impose the death penalty in decades.

Smith began his legal career in the 1990s in the Manhattan District Attorney’s office where he handled sex crimes and domestic violence cases. In 1999, he moved to the Eastern District of New York in Brooklyn, where he was part of a team that prosecuted an NYPD police officer accused of lying about torturing a Haitian immigrant in a precinct bathroom.

“Gangsters, cops and war criminals, these are the kinds of cases he’s worked on during his career and those are some of the toughest cases to prosecute,” said Alan Vinegrad, who was acting Brooklyn U.S. attorney in 2002 and is now a partner at Covington & Burling LLP.

Vinegrad and Smith prosecuted the NYPD case together.

Allowing a special counsel like Smith to handle the Trump probes may protect the government from potential conflicts of interest and avoid allegations of bias, and Smith is expected to operate largely independently from Justice Department leadership.

Smith will oversee the investigations into the Jan. 6, 2021, insurrection at the U.S. Capitol – including any role that Trump may have played – as well as the former president’s handling of classified White House records after he left office.

When Smith ran the Public Integrity Section from 2010 to 2015, James Trusty, now a Trump attorney working on the Mar-a-Lago case, was chief of the Criminal Division’s Organized Crime and Gang Section from late 2010 to early 2017. He did not immediately return a request for comment.

Since 2018, Smith has served as the chief prosecutor for the special court in The Hague charged with investigating and adjudicating war crimes in Kosovo. This was his second stint there: He left Brooklyn for The Hague in 2008 to be the investigation coordinator in The Hague, overseeing investigations of militia members wanted for war crimes and genocide.

“He’s done high-profile cases and has the skill set and judgment to make the charging decisions in a case and back them up in a courtroom,” said Greg Andres, a former federal prosecutor in Brooklyn who was later on Special Counsel Robert Mueller’s team that investigated foreign meddling in the 2016 presidential election.

Smith returned to the U.S. in 2010 and for five years ran the Justice Department’s public integrity section, which investigates corruption allegations against public officials. While there, Smith oversaw the prosecution of former New York Assembly Speaker Sheldon Silver, who was convicted of taking nearly $4 million in illicit payments.

“He was one of the best investigators in the office, understanding what gaps needed to be filled in a case, giving clear instructions to investigating agents which is why they loved working with him,” said Kelly Currie, who served as interim Brooklyn U.S. attorney after Loretta Lynch became attorney general in 2015.

Currie, now a partner at Crowell & Moring LLP, said after Smith became a supervisor he started a moot trial that allowed prosecutors to give their cases a dry run in a practice still in place today.

Smith left Washington for Tennessee in 2015, eventually serving as first assistant U.S. attorney and then acting U.S. attorney in Nashville until 2017. He briefly worked as a top lawyer for HCA Healthcare, returning to The Hague in 2018.

Upon departing Nashville, Smith said in a news release it was “one of the most difficult professional decisions that I have ever been faced with. I truly love representing the American people and seeking justice on their behalf.”

A varsity football and baseball player who grew up in Clay, New York, he’s a graduate of SUNY Oneonta and Harvard Law School. During his time as a Brooklyn prosecutor, he was known as an accomplished triathlete and an avid cyclist.

In announcing the appointment Friday, the Justice Department said Smith would remain in the Netherlands in order to recover from a recent bicycle accident.