As Hezbollah rained rockets on Israeli cities this summer while hiding behind Lebanese human shields, Human Rights Watch carried on a parallel political war against the Jewish state. Human Rights Watch released only one substantive report on crimes committed during the war, and that report was aimed squarely at Israel.

Now, as Iran rearms Hezbollah for a renewed military campaign against Israel, Human Rights Watch also has resumed its offensive. Shortly before Christmas, the group released a 24-page report that attempts to rescue its earlier accusation that “On July 23, at 11:15 p.m., Israeli warplanes struck two clearly marked Red Cross ambulances in the village of Qana.”

Based on photographic evidence of the ambulances that was inconsistent with the allegation, third parties, such as Australia’s foreign minister, labeled the alleged incident a clear “hoax.” That the group, which styles itself as an objective investigative human rights organization, accepted the claim without question is troubling.

Attempting to salvage its credibility following extensive criticism of its summer report, Human Rights Watch dispatched researchers to Lebanon to collect evidence on the alleged event. The new report summarizes their findings.

“Human Rights Watch originally reported that the ambulances had been struck by missiles fired from an Israeli airplane, but that conclusion was incorrect,” the report states. The Lebanese ambulances could not have been struck by missiles fired by an Israeli warplane “as such missiles would have caused much more massive destruction and have left a huge crater.” Additionally, “the limited damage caused, and the non-existence of heavy shrapnel, also rule out an artillery-fired round.” Moreover, “none of the witnesses reported hearing helicopters in the air before or during the attack.” And the researchers found no “diagnostic shrapnel or missile parts in the street.” The report contains no evidence whatsoever of any other Israeli presence in the area that could have attacked the ambulances.

Yet, Human Rights Watch buries these critical admissions in the middle of the document and instead headlines the report with a claim that the group did no wrong. “On the basis of this investigation,” the report says, “we conclude that the attack on the ambulances was not a hoax: Israeli forces attacked two Lebanese Red Cross ambulances that night in Qana, almost certainly with missiles fired from an Israeli drone flying overhead.”

What is the evidence for the new allegation of an Israeli drone attack using missiles? The report makes clear that there is none. This time, Human Rights Watch is not being duped by a fabrication — it is the fabricator.

The report presents nothing more than its conjecture that Israel possesses and used unspecified new “limited impact missiles designed to cause low collateral damage” fired from drones. It points to the existence of holes in the roadway, which it asserts — without forensic or any other evidence — were caused by the conjectured missiles.

Human Rights Watch cannot identify any missile that would cause damage consistent with the condition of the ambulances and admits that there is no physical evidence of any Israeli missile of the imagined “limited impact” variety or of any other type. Nevertheless, the report speculates that such a missile exists because Israel has sophisticated weaponry. The report refers to Israeli SPIKE missiles and to American DIME missiles — Al-Jazeera accuses Israel of using the latter — but neither type of missile has an impact signature consistent with the physical condition of the ambulances.

Further, Human Rights Watch doesn’t present any evidence of witnesses having heard or seen a drone or of Israel having used drone-fired missiles during the war. And the group doesn’t adequately explain the advanced rust corrosion of the ambulances — which actually indicates that any such damage occurred many months prior to the war. The group did not order any expert examination of the vehicles, yet the report asserts that the “saline humidity of Lebanon’s coast causes rapid rusting, especially on damaged metals.” The group continues to rely upon the testimony of witnesses like Qasim Cha’lan whose report of “a boom” and “a big fire” is contradicted by the physical evidence.

Instead of offering evidence, the new report speculates about what might have happened and dwells on irrelevant details, such as the travel itinerary of its personnel in Lebanon.

The report concludes by reasserting on page 24 what it admitted on page 12 was untrue: “In conclusion, … All of the available evidence shows that the Israeli attack which hit the Qana ambulances took place as reported.”

As during the summer, Human Rights Watch assumes Israeli guilt without proof, viewing its mission as constructing a scenario, however implausible, in which it might be right.

This approach has the perverse effect of encouraging future war crimes and human rights abuses because it convinces war criminals like Hezbollah that their crimes will go unpunished with Human Rights Watch’s support.

During the summer war in Lebanon, Hezbollah committed thousands of war crimes, including using civilians as shields, indiscriminately attacking Israeli civilians, and pretending to be civilians and other protected persons. Lebanon violated Security Council Resolution 1373 — adopted under Chapter VII of the U.N. Charter and therefore legally binding — by providing Hezbollah with a safe haven. Lebanon, Syria, and Iran violated their obligations under Resolution 1373, the Genocide Convention, and the Hague and Geneva Conventions not only by failing to prevent and punish Hezbollah’s actions, but also by providing financial, military, and logistical support.

In portraying Israel as the perpetrator, rather than the victim, of war crimes, Human Rights Watch encourages violation of the very legal standards that it purports to uphold. By rejecting legitimate criticisms, Human Rights Watch demonstrates that it is not a credible reporter or advocate of human rights.

Mr. Bell, a member of the faculty of law of Bar-Ilan University, is a reserve staff sergeant in the Israel Defense Force and served in combat during the summer war in Lebanon.