Kahl responded by connecting Gavrilo with school administrators. But Gavrilo's reply made it clear that she wanted to meet only with Kahl.
At that point Kahl mentioned the exchange to her husband, Colin, who had been an assistant to President Barack Obama and national security adviser to Vice President Joe Biden. They agreed that it smelled fishy, and Rebecca stopped responding. The exchange died.
A year later, it turns out that the Kahls were right: Something was amiss. Gavrilo was a fake identity, one of several assumed by an operative working for Black Cube, a shadowy Israeli private security firm.
Internal Black Cube documents obtained by NBC News and interviews of sources with direct knowledge of Black Cube's operations reveal a business intelligence company with governmental contracts and a special department for politically motivated work.
A source familiar with Black Cube's outreach to the Kahls told NBC News that it was part of an effort to discredit Obama administration officials who had worked on the Iran nuclear deal - and, by extension, the deal itself. Black Cube sought evidence of nefarious behavior, such as financial or sexual impropriety, by the deal's architects, including Colin Kahl. Operatives hoped to obtain such evidence by befriending their targets or their targets' associates.
Also targeted was Ben Rhodes, a deputy national security adviser under Obama, whose wife, Ann Norris, was approached by a Black Cube operative about consulting on a political drama for TV. Norris had previously worked at the State Department.
The undercover campaign to discredit the Iran deal was first reported by the British newspaper The Observer and by The New Yorker.
In a statement to NBC News, Black Cube said it has no relationship to the Iran nuclear deal.
"Anyone who claims otherwise or anyone suggesting Black Cube is targeting U.S. officials is misleading their readers and viewers," the statement said.
"Luckily," it continued, "the Mossad and the CIA are capable to deal with the Iran nuclear deal and other issues of national security without relying on the expertise of Black Cube."
The firm added that it "always operates in full compliance of the law in every jurisdiction in which it conducts its work."
In the end, Black Cube's Iran-deal spying yielded no compromising information, and in early May, Trump announced the U.S. would withdraw from the nuclear deal. But the use of the shadowy firm continues to draw scrutiny. On Friday, Democratic members of the House Oversight Committee wrote to the founders of Black Cube requesting documentation related to its Iran work.
Marketing its links to Israeli intel
Black Cube made headlines last fall after revelations that it had been hired to intimidate and disparage accusers of Harvey Weinstein, as well as reporters investigating the Hollywood producer.
The firm was founded by former Israeli military officers in 2011. It retains close ties to the Israeli intelligence community, and many of its recruits are former Mossad agents.
Those links are part of its pitch to clients.
"The insinuation is that 'we're so powerful, we have these links, and we can call on them,'" said the source, who asked not to be identified, fearing reprisal from Black Cube. "They want that veneer of 'we're still the state, but we're not really the state.'"
The firm has two divisions: one catering to corporate clients and one to governments and political actors.
Its website advertises its corporate work, such as performing due diligence on clients' competitors or acquisition targets. "We help our clients identify their adversaries' sensitive points or vulnerabilities, or evidence of their misconduct," its website reads. It boasts of its ability to provide "otherwise unobtainable information."
Its government work has occasionally landed Black Cube at the center of sensitive political disputes across the globe, while raising serious ethical and legal questions. For example, in Romania, two Black Cube operatives were arrested on suspicion of spying on the country's anti-corruption prosecutor in 2016.
"When the Romania affair came out in the news, several people on the corporate side left," said another source — a former Black Cube insider — who spoke on the condition of anonymity since he also feared reprisals. "It created a rift in the company and several people quit almost immediately."
The campaign to discredit the Iran deal is the first public case of the firm's apparent meddling in U.S. politics.
Black Cube's political work frequently intersects with Israel's foreign policy priorities. Israeli Prime Minister Benjamin Netanyahu, for example, has campaigned vociferously against the Iran deal.
"They would never work against Israeli interests," said the source who was familiar with Black Cube's Iran work. He likened the firm to an "almost privatized wing of Mossad."
He also suggested there was little chance that the Israeli government or its intelligence agencies were unaware of Black Cube's work to discredit the Iran deal.
The same source said the Iran operation was launched just days after President Donald Trump visited Israel in May 2017. The source said he was told that the work was being carried out "for Trump," but there is no evidence that the Trump administration had anything to do with the operation, which may have been commissioned by an outside group or agency with no connection to the administration. The identity of Black Cube's client on the Iran work remains a mystery.
"You'll never find their name on a contract," the source said. "I can't prove that it was the administration other than what I was told."
But, he added, "Why spend time and money to make the whole the deal look rotten, unless you're obsessed with destroying Obama's legacy?"'
The Black Cube statement said the company "has no relation whatsoever to the Trump administration, to Trump aides, to anyone close to the administration, or to the Iran nuclear deal."
The White House did not respond to a request for comment.
A 'nasty, nasty business'
In their first joint interview about the undercover operation, the Kahls expressed dismay at Black Cube's tactics. Colin called it a "nasty, nasty business." To come after him through his wife and daughter "crosses so many lines," he said.
NBC News obtained Black Cube's research file on the Kahls, which contained their address, the names of their relatives and other personal details. But it also had mistakes, such as the make of their car and their daughter's birth year.
"It's creepy to know that someone was trying to dig up your profile and the names of your in-laws and your kids and your wife and where you live," said Colin, when presented with the file. "That's pretty sleazy."
The idea that the couple could be the target of a foreign intelligence operation had occurred to the Kahls, but it seemed unlikely with Colin out of government. "We're also just not that important of people," Rebecca joked.
When asked why Black Cube didn't target others more senior in the Obama administration, the source familiar with the firm's Iran work explained that Kahl and Rhodes were more accessible targets. "It's easier to get to people lower down."
Kahl said it wasn't entirely surprising that he and Rhodes were targeted despite the fact that others higher in the Obama administration had helped craft the Iran deal.
The two had become something of a "fixation" for members of the Trump administration, Kahl believes, thanks to their active social media presence and willingness to be quoted in the press criticizing the president.
"There was this kind of fever dream that emerged among a number of senior aides to President Trump," said Kahl, "which was that Ben and I were actually responsible for being the puppet masters behind the deep-state conspiracy to undermine the president and leak things."
Indeed, Trump adviser Sebastian Gorka decried the "Ben Rhodes-Colin Kahl nexus" in an interview on Fox News in May 2017. Then in June, the conservative Washington Free Beacon quoted an anonymous Trump Administration official singling out Kahl and Rhodes for leaking to the press.
As part of its work on Iran, Black Cube also targeted journalists and advocates of the Iran deal working outside government, according to documents obtained by NBC News. One of those documents was a Black Cube list of reporters whose work often dealt with Iran, including Andrea Mitchell, NBC's chief foreign affairs correspondent.
Another target of Black Cube, according to the documents, was Trita Parsi, a Swedish-born Iranian who heads the National Iranian American Council, a Washington nonprofit group that backed the nuclear deal. Parsi says that he was warned by someone within the U.S. intelligence community, through an intermediary, that he was a likely target for critics of the deal.
Sure enough, a Black Cube operative, posing as a reporter, called Parsi about a year ago and pressed him on whether anyone within the Obama administration had profited financially from the deal. NBC News obtained audio and a transcript of the call.
When Parsi denied that financial incentives had motivated the deal, he said the operative "just gave up and cut the interview short."
A now-familiar playbook
Black Cube's tactics relating to the nuclear deal - including its use of aliases and its targeting of journalists - resemble its approach in its work for other clients.
As part of the company's work for Weinstein, a Black Cube operative befriended the actress Rose McGowan while posing as an investment manager focused on women's empowerment at a London-based firm, according to emails between her and McGowan obtained by NBC News. The operative used the alias Diana Filip in the Weinstein scheme, according to the emails. That bogus firm was the same that Gavrilo, in reaching out to Rebecca Kahl, claimed as her employer.
The identity of Diana Filip was revealed to be an Israeli army veteran named Stella Penn Pechanac by the British tabloid The Daily Mail.
Elsewhere, Black Cube's underhanded tactics have been revealed to the embarrassment of its clients.
Hired by a Canadian investment company in a dispute with another firm, a Black Cube operative attempted to embarrass an Ontario superior court judge who had ruled unfavorably for Black Cube's client by trying to induce him to make anti-Semitic comments. The effort went nowhere, and Black Cube's client in that case is now mired in lawsuits.
Rebecca Kahl said her experience as a Black Cube target felt like what life would be like in an authoritarian country, where civil society groups and political activists are routinely harassed.
"It certainly has an authoritarian feel to it - to target your political opponents or try to smear them or discredit them," she said.
For his part, the source familiar with Black Cube's Iran work believes that all the recent publicity around the company will only bring in more clients. "The more we talk about it, the more business they get," he said.