Jonathan Lenzner is taking over leadership of Investigative Group International from his father, Terry. The D.C.-based private investigation business was founded in 1984. (Jocelyn Augustino)

Speaking to a crowd of lawyers, computer hackers, retired intelligence analysts and former journalists on a rooftop overlooking the White House, Terry Lenzner does not look like he’s ready to hang it up. He works the crowd with warmth but looks you in the eye with the intensity of an interrogator.

But onOct. 8, Lenzner, 76, gathered some of his closest associates to announce that he is handing over leadership of Investigative Group International to his son Jonathan.

Terry stepped down last spring from day-to-day operations, but he says he will be “certainly on hand to jump in when needed,” and will still help shape the direction of the firm as owner and chairman.

A former Watergate attorney who served a subpoena on Richard M. Nixon, Lenzner founded his private investigation business in 1984 with the help of three journalists (two of them came from The Washington Post) and filled out the ranks with sleuths of all sorts.

He hired former FBI deputy director Larry Potts, former intelligence analysts such as current managing director Robert Mason, and law enforcement officials such as former New York City Police Department commissioner Raymond Kelly. He also liked former journalists, whose skills at wheedling out information in informal settings struck a contrast to the more methodical pace of the typical prosecutor, who tends to rely on the power of the subpoena.

Lenzner’s tactics were more gumshoe. At one point his company paid janitors to obtain trash containing Microsoft’s corporate secrets on behalf of competitor Oracle. And he famously dug up dirt on women who brought ­sexual-misconduct allegations against Bill Clinton.

The boutique firm, which can charge $100,000 for a big investigation, still runs a steady business in Washington’s hallways. Today, it has 50 to 60 cases open at any given time, one-third of them large projects such as an internal investigation at a large corporation. The rest are small due diligence cases for which the company typically charges tens of thousands of dollars. Some regular clients pay a monthly retainer.

In recent years, the company has run into competition from unexpected places. The District’s big law firms, which are responsible for about half of IGI’s referrals, are increasingly getting in on the investigations game. Terry’s co-founder Jim Mintz spun off his own investigative firm in 1994, and New York-based Nardello and Co. follows a similar business model.

As its been outflanked by competitors, IGI has doubled down on its legacy clients.

“They never argue that what we are going to do costs too much money,” said Bob Kelso, chief executive of Forensic Pursuit, an electronic-evidence-gathering firm that partners with IGI on investigations. “They want the job done, and they’re willing to pay the price to get high-end work done.”

In its heyday, the company’s ranks swelled to 130 employees across multiple cities, but Lenzner hated having to manage a workforce.

Bringing in business was his thing — a “rainmaker,” his son says.

“Terry was a good leader in the sense that he could motivate people, attract clients and build a following,” Jonathan said. “His employees love him, hate him and at times both love him and hate him.”

“But,” the son said, “he was not a good businessman and not a great manager.”

So who is Jonathan Lenzner?

For starters, he is his father’s son.

“My father and I have always had a good relationship, but I knew it would be a challenge to work with family,” said Jonathan, 42. “So I never really wanted to work with him, but I did want to learn from him.”

He started his career in a different sort of role on Capitol Hill, as a press secretary for a Connecticut congressman. He went on to work for Democratic presidential candidate Bill Bradley ahead of the 2000 elections. Drawing on that experience, Jonathan adds crisis communications to IGI’s portfolio, a shift for a firm that built its name on fact-finding missions. In the past eighteen months, at least eight of the firm’s new cases have veered into media strategy.

“A lot of lawyers don’t understand the media, how quickly it moves now and how aggressive you need to be,” Jonathan said.

He talks like a PR operative, hopping off- and on-record like someone who knows his way around the media.

He also draws on prosecutorial experience. After graduating from law school in 2004, Jonathan served in the Manhattan district attorney’s office for six years, taking on everything from public corruption and financial fraud to sex trafficking.

He moved to the District in 2010 to work in the Maryland U.S. attorney’s office, and moved on to his father’s firm in 2013. (Jonathan is married to a Post reporter who did not contribute to this article.)

“I had never thought I would join the business,” he said. “When I did join, it was because it was a unique opportunity to make a brand better.”

The firm has typically found its business through word of mouth in Washington’s power circles. Jonathan says he wants to get more aggressive about marketing while still prioritizing loyalty over outreach.

“He’ll pass up a buck to make sure his client’s interest is what’s motivating him rather than revenue,” said Benoit Flippen, principal security consultant at ­FusionX, a Reston-based cybersecurity company that has partnered with IGI.

The partnership with ­FusionX suggests that Jonathan could be taking the firm ­high-tech, a departure from the ­old-school, shoe-leather information gathering it has relied on in years past. FusionX employs “expert hackers” to simulate data breaches, identifying security vulnerabilities by breaking into a client’s network.

Terry Lenzner says things fell into place when his son returned to the District after a decade-long career as a prosecutor.

“I didn’t start it to be a family business, but my family — my children, my wife — have been a part of IGI at one time or another,” Terry said. “Bringing him in with the idea of having him run things seemed like the natural thing to do.”

He will be following the legacy of his father’s storied reputation. Terry’s interviewing style earned him the moniker “Terrible Terry,” which lit up the media after a 1972 Watergate hearing. Terry was the deputy counsel to Samuel Dash, the chief counsel on the Senate Watergate Committee.

“He could always change the mood in a room, and not always for the better,” Jonathan said.

As Terry relates in a 2013 memoir, White House aide Richard Moore was called to the stand as a surprise witness. Despite having less than an hour to prepare for the interview, Terry grilled the man so mercilessly that a New York Times columnist accused him of running a “vicious attack,” suggesting that the young lawyer was “bedazzled” by his moment “in the limelight,” using it to make an example of Moore.

“The hearings became their own kind of soap opera, in which many viewers saw an aggressive young man picking on a nice old man, and they didn’t like it,” Terry wrote in his memoir.

The event would be remembered as a defining moment of the hearings.

As for Jonathan, having the same last name as one of the most feared men in Washington came with its share of odd encounters around town.

One summer when he was in law school, he sat during a ­dinner party and realized mid-conversation that he was talking to the granddaughter of Moore, the man his father had interrogated on national television.

She and her family did not have fond memories of Terry or the fallout from the interview.

“My grandfather was never the same after the White House investigation,” the young woman told Jonathan.

When he started talking about his own family, there was a long pause.

“I know exactly who your father is,” she said.

The conversation ended there.