I am trying to find MSM that says they are friends. (This has nothing to do with my feelings about Barr and if he should recuse from this new case.)
I did find this:
U.S. Attorney General William Barr
From Clinton To Trump: The Powerful Men In Jeffrey Epstein's Orbit
U.S. Attorney General William Barr served as counsel for the law firm Kirkland & Ellis, which was part of Epstein's legal team in 2007 and helped him obtain his plea deal. Barr is not recusing himself from the current case against Epstein, but he "has been and will remain recused from any retrospective review of the resolution of the earlier case in Florida," according to CNN reporting.
Accused Sex Trafficker Jeffrey Epstein’s Political Connections: A Guide :
Attorney General Bill Barr and Epstein go way back: back in the early 1970s, Barr’s father hired Epstein to work as a physics and math teacher at the elite Manhattan private school Dalton, despite the fact that Epstein did not have a college degree. Following Epstein’s arrest, former FBI assistant director Frank Figliuzzi hinted that Barr could “attempt to interfere” with the prosecution of the case, though this would be unlikely given the “obvious” link between the two men. During his confirmation hearings, Barr himself said he would likely recuse himself from any involvement with the Epstein case, as he previously served as counsel for the law firm Kirkland and Ellis, which also represented Epstein in negotiating the terms of his 2007 plea agreement. But in an essay for the Daily Beast, former federal prosecutor Mimi Rocah expressed concern that Barr wouldn’t keep his word in this regard: “while it pains me to say this, given Barr’s conduct in the past acting more as a defense attorney for Trump than an overseer of justice, I am concerned that Barr might interfere if he thought that Epstein might implicate Trump, who was friends with Epstein,” she wrote.
In the article you linked to above, with interviews with students from the Dalton school, it mentions Epstein's hiring by and friendship with Barr's father. It also quotes some of the students talking about how AG Barr used to attend school/social events at Dalton School with his father and that students were familiar with him back then. There was some mention of AG Barr playing bagpipes or something at school functions. It also sounds like faculty socialized with Barr's father, so assume there were numerous occasions when AG Barr socialized with Epstein.
Given Epstein's subsequent activities with many DC politicians in later years, it's safe to assume he encountered AG Barr again in later years and knew him through mutual friends. Epstein was very active in those social circles and DC is a "company town". So, it seems prudent to review their relationship over the years with an eye to asking Barr to recuse himself. If they place a gag order on the current federal case and cut off public access to information about allegations against Epstein, that should also be a red flag. All JMO of course.