After Jeffrey Epstein was indicted for sex crimes in 2006, his Harvard lawyer, Alan Dershowitz, called on the expertise of one of his Harvard colleagues, famous linguist Steven Pinker.

An obscure document from Epstein’s legal defense shows that Pinker weighed in on the precise meaning of a federal law about using the internet to entice minors into prostitution or other illegal sex acts.

“Though I did this as a favor to a friend and colleague, and not as either a paid expert witness or as a part of a defense team, knowing what I know now I do regret writing the letter,” Pinker said by email.

Epstein, who had donated millions of dollars to Harvard, seemed to relish his connections to the university. He once served on Harvard’s Mind, Brain, and Behavior Advisory Committee, and press releases issued by his charitable foundation billed him as a “Harvard philanthropist” and a “Harvard investor.”

When Epstein was indicted in 2006, Dershowitz, a personal friend, joined his defense team. As Dershowitz researched the charges, he asked Pinker for advice on the wording of a federal law sometimes known as the “internet luring statute.”

In a July 2007 letter to US attorneys prosecuting the case, Dershowitz and another of Epstein’s lawyers, Gerald Lefcourt, argued that law didn’t apply to Epstein because prosecutors had not specifically shown that Epstein had used online communication to entice the unidentified victims of his alleged crimes.

“To confirm our view of the ‘plain meaning’ of the words, we asked Steven Pinker … a noted linguist, to analyze the statute to determine the natural and linguistically logical reading or readings of the section,” the pair wrote. “Specifically, we asked whether the statute contemplates necessarily that the means of communication must be the vehicle through which the persuading or enticing directly occurs. According to Dr. Pinker, that is the sole rational reading.”

Pinker said that over the years he has regularly offered his linguistic opinions to Dershowitz for use in various cases. “I don’t recall his telling me that the question pertained to the Epstein defense,” Pinker said. “I was not aware of the charges against Epstein at the time. And no, I was not paid for the letter — it’s something that Alan and I do regularly, as colleagues.”

Dershowitz said he didn’t remember Pinker’s involvement until seeing the document again. “My expertise was in the relationship between law and science, so it was natural that I would call on Pinker,” Dershowitz told BuzzFeed News.

Pinker, who responded this week to criticism for being photographed with Epstein during lunch at a meeting at Arizona State University in 2014, told BuzzFeed News on Thursday that “I could never stand the guy and always tried to keep my distance.”

Whether the arguments from the high-powered combination of Harvard lawyer and Harvard linguist on the meaning of “using” held much sway in the plea deal eventually negotiated between federal prosecutors and Epstein’s legal team is unclear.

“It was one among many arguments as to why the statutes were not applicable,” Dershowitz said. “In the end, the reason we got the deal we did is we had many persuasive arguments.”

Under the plea deal, all of the federal charges were dropped. Epstein pleaded guilty to state charges of soliciting a minor for prostitution and served 13 months in a Florida jail (although he was allowed out during the day to continue managing the investments of his billionaire clients).

In light of the new federal charges of sex trafficking brought this week, the earlier deal has faced widespread criticism for its leniency. That culminated earlier today with the resignation of Labor Secretary Alex Acosta, who was the US attorney for the Southern District of Florida when Epstein’s plea deal was agreed.

Dershowitz is not involved in Epstein’s current defense and said he has not been in recent contact with his former client.