A professor of public international law is being investigated by Copenhagen University following a series of tweets that he made about UK Lawyers for Israel (UKLFI).

Prof. Heller, who is also a Special Adviser to the Prosecutor of the International Criminal Court (ICC) on War Crimes, an editor of the international law blog Opinio Juris, and a member of Doughty Street Chambers, wrote a short thread of posts on X (formerly Twitter) on 2 December 2024.

The thread referred to criticisms by UKLFI of allegations made by the ICC Prosecutor in support of his applications to the Pre-Trial Chamber for warrants for the arrest of the Israeli Prime Minister, Benjamin Netanyahu, and former Defence Minister, Yoav Gallant.

UKLFI’s criticisms had been set out in detail in a 25-page letter to the ICC Prosecutor and a 13-page annex, between them containing 188 footnotes referring to extensive evidence. Both were published by UKLFI on its website on 29 August 2024 and publicised on X. They could easily be located with minimal research at all times since then.

UKLFI’s letter to the Prosecutor noted that the applications themselves had not been published, but the Prosecutor had summarised his allegations in a pre-prepared, formal statement published in writing and as a video recording on the ICC’s website – where it is titled and described as a “Statement of the ICC Prosecutor” and differentiated from “Press Releases”.

The Prosecutor’s statement referred to a Report of a Panel of Experts, also published on the ICC’s website, which provided additional information about the applications.

UKLFI’s letter to the Prosecutor stated that UKLFI assumed that the Prosecutor’s statement provided a fair and accurate summary of the applications, but if it did not, the statement itself breached applicable professional rules.

UKLFI’s letter showed meticulously that every phrase of every sentence of the Prosecutor’s summary of his allegations was false. It also showed that these allegations were contradicted by additional evidence that came into existence subsequent to the applications, which could not have been included in the applications, but the Prosecutor had declined to update the Pre-Trial Chamber.

UKLFI has not received any communication disputing any element of its analysis.

In his thread of posts on X, Prof Heller alleged:

“It should surprise precisely no one that UKLFI’s vexatious, dishonest attacks on the Court and the OTP were made in partnership with the Israeli government.

These are, of course, the same lawyers who accused @KarimKhanQC of making false statements in the applications for arrest warrants despite not having access to the applications themselves. UKLFI made the allegation based on a *press release*.

And they are the same lawyers who filed a complaint with the UK bar accusing Andrew Cayley KC of misconduct based on nothing more — and I am not making this up — than him standing behind the Prosecutor when the Prosecutor announced he was applying for the arrest warrants.”

UKLFI promptly emailed Prof Heller the same day asking him to take down his defamatory posts. UKFLI pointed out that its complaints were set out in detail in its published letter and annexes, that it honestly believes the points it has made are true and valid, and that they were not made vexatiously to annoy. On the contrary, UKLFI made the complaints because it genuinely believes that the Prosecutor’s allegations are false, that he has failed to provide to the Court material contradicting his allegations, and that these defects should be corrected.

UKLFI added that its analysis was based on material in the public domain and that it had no partnership or other agreement with the Israeli government.

UKLFI observed that the Prosecutor’s formal statement announcing his filing of the applications for arrest warrants was not a mere “press release”, as Prof Heller claimed.

UKLFI also noted that its complaint to the English Bar Standards Board (BSB) regarding Andrew Cayley KC was based on rather more than that he stood behind the Prosecutor when the latter made his formal announcement of the applications for the arrest warrants.

In particular, UKLFI’s complaint to the BSB (also published on its website) referred to the Prosecutor’s statement in an interview by the BBC that Brenda Hollis and Andrew Cayley had led the investigation. Moreover Cayley’s appointment to oversee the investigation had been reported in The Guardian on 11 March 2024 and must be known by Prof Heller.

Prof Heller did not reply to UKLFI’s email and did not take down the posts. UKLFI therefore made a complaint to Copenhagen University. The University has confirmed that it is investigating the complaint but will not inform UKLFI as to the outcome.

Jonathan Turner, chief executive of UKLFI, said: “Prof. Heller is entitled to express a good faith disagreement with our analysis (although we think it is very strong), but he is not entitled to publish entirely false and unfounded allegations.”