The investigation, done in conjunction with the United States Marshals Service, was launched after allegations that Mengele was at any time in the custody of or had any relationship with U.S. government institutions or personnel after World War II.

Posner, and his wife, Trisha, traveled to Hong Kong, the Golden Triangle, the Netherlands, San Francisco, London and New York to conduct in-person research with drug traffickers.

Karen Stabiner wrote in her review for the Los Angeles Times, "This is a mesmerizing, blood-chilling book, a set of oral histories of the sons and daughters of 11 of Hitler's top men.

[25] In his 2003 autobiography, Producer: A Memoir, Wolper cited his failure to get movies made of Case Closed and the Cuban Missile Crisis book, One Hell of a Gamble: Khrushchev, Castro, and Kennedy, as his two major career disappointments.

[27] In 1998, the Assassination Records Review Board briefly referenced this testimony in discussing two unsuccessful attempts to acquire the interview notes of two physicians, James Humes and J. Thornton Boswell, that Posner said he possessed.

[28] Case Closed generally drew critical acclaim from the media; the Chicago Tribune, the Toronto Sun, The Sydney Morning Herald and Newsday all cited Posner's "meticulous" research in their respective reviews.

[29] In his review for the Chicago Tribune, Jeffrey Toobin wrote, "Unlike many of the 2,000 other books that have been written about the Kennedy assassination, Posner's Case Closed is a resolutely sane piece of work.

The book concluded that confessed assassin, James Earl Ray, killed Martin Luther King Jr. acting alone, likely for the hope of collecting a racist bounty for the murder.

[49] As was Case Closed, Killing the Dream was widely praised and embraced by the mainstream press, and among the national broadcasts that featured the book included CBS' 48 Hours, Charlie Rose and TODAY.

[56] In 1999, the King family, represented by Pepper, brought a civil lawsuit in which a jury found evidence of a conspiracy involving Loyd Jowers, the owner of a restaurant near the assassination site.

"[58] Most of the mainstream press echoed the San Francisco Chronicle which concluded that "Posner offers the most objective and thoroughly accurate history of the label to date, plus a detailed and complex portrait of its founder, Berry Gordy".

This assertion was strongly denied by Prince Ahmed's family, who pointed out that he in fact loved the U.S., spent time at his home there, and invested heavily in the U.S. horse racing industry.

Connection, Posner provides an account of the "close" business and personal relationship between the House of Saud and the U.S. government, including discussions of "dirty bomb" technology and the financial and political maneuvering surrounding 9/11.

In a New York Times review, Byron Burroughs said: "Where Posner thrives is telling the stories of the first developers and artists who foresaw what Miami Beach would become and worked against all odds to build it.

The cumulative effect of Posner's detective work is an acute sensation of disgust—along with a mix of admiration for and skepticism about Pope Francis' efforts to reform the Vatican Bank and its curial enablers.

"[79] Some reviewers have noted that God's Bankers contains inaccuracies, the most serious of which is Posner's allegation in Chapter 11 that Bernardino Nogara, the wartime director of the Vatican's Amministrazione Speciale per la Santa Sede, was a Nazi intelligence agent.

[82] Citing disclosures in God's Bankers, Posner wrote an opinion editorial in the Los Angeles Times on February 13, 2015 calling on Pope Francis "to approve the release of the Vatican's Holocaust-era files in its secret archives.

"[86] Literary Hub selected PHARMA as one of the "most anticipated books of 2020," and in a review, author John Freeman stated: "The cat’s out of the bag on this one, we all know pharma has been a disaster for many Americans, but Gerald Posner specializes in telling you what you don’t know: in his New York Times bestsellers like Case Closed and books like Hitler’s Children or God’s Bankers, what he has perfected is achieving the kind of disgust only a massive research dive can bring.... Posner has created a medical leviathan for our times.

"[87] Beth Macy, author of Dopesick, says that "I could not put down Gerald Posner’s Pharma, the definitive story of how one family, the Sacklers, set out to get exquisitely rich on the back of unsuspecting Americans—then blamed the so-called 'abusers' instead of their own highly addictive drug.

In the Los Angeles Times he argued for the appointment of an independent examiner in the bankruptcy of Purdue Pharma so that the case would not leave "unanswered the many troubling questions about the full extent of the [Sackler] family’s role in igniting and fanning the opioid epidemic for its own profit."

Besides the Sacklers and Purdue Pharma, Posner joined Margarida Jorge, the campaign director for Lower Drug Prices Now, in a Newsweek opinion piece that criticized pharmaceutical executives for profiting from rumors and press releases about COVID-19 vaccines and treatments.

Posner wrote that "The Biden administration should avoid rewarding any government official who contributed to the opioid crisis having become the most lethal prescription drug epidemic in American history.

[100][101] He was also the consultant to Inheritance, a 2006 documentary about the story of Monika Hertwig and her effort to grapple with the enormity of the crimes of her father, Kraków-Płaszów concentration camp commander, Amon Göth.

It was there that he became involved in an ultimately unsuccessful 4-year pro bono effort on behalf of victims of concentration camp experiments against the West German government and the family of Nazi experimenter Josef Mengele.

[108] Posner provided pro-bono advice to Viktor Bout, the Russian arms dealer nicknamed in the press as the "Merchant of Death" (played by actor Nicolas Cage in the film Lord of War).

[110] In 1999, in the premier September issue of Talk Magazine, Posner wrote about the mistakes of French and British investigators in the 1997 death of Diana, Princess of Wales ("Al Fayed's Rage").

According to Posner, "an active U.S. intelligence asset" let him listen to "an innocuous portion of an undated conversation between [Princess] Diana and di Lima (the wife then of the Brazilian ambassador to the United States)."

In 2006, Scotland Yard released The Operation Paget Inquiry Report Into the Allegation of Conspiracy to Murder: Diana, Princess of Wales and Emad El-Din Mohamed Abdel Moneim Fayed.

For instance, the American investigative writer Gerald Posner says in the report that through a source, he heard an intercept of a telephone call between Diana and Lúcia Flecha de Lima, wife of the Brazilian ambassador at the time.

Lee claimed that Samuel Pinkus, her literary agent's son-in-law, tricked her into signing away her rights to To Kill a Mockingbird, directing the royalties to be paid into a corporation formed by Posner for that purpose.