"It demonstrates a lack of understanding as to how the International Criminal Court functions. Ismaili does go on to add that the US could be prosecuted in Iraqi courts and in the Supreme Court of Iran, which is more feasible, albeit unlikely, than the ICC," Cadman said.
The lawyer explained that the ICC only had jurisdiction to investigate situations within the territory of state parties, which are the countries that have ratified the Rome Statute of the International Criminal Court, or against citizens of state parties.
"Neither Iran nor the United States are state parties. Second, it can investigate situations that have been referred to the ICC by the UN Security Council. Considering that the United States is one of the five permanent members and has the power of veto, that is unlikely in the extreme," he said.
The third option would be if a state refers itself to the ICC in case the alleged crime passes a certain gravity threshold.
"This is an option open to Iran. It is most unlikely, as should Iran refer itself to the ICC, it would then be open to investigation for its own conduct in Syria, Yemen and Iraq. It is unlikely to see this as a viable option for the killing of Soleimani," Cadman said, adding that a single killing would not pass the gravity threshold.
Moreover, the lawyer said that turning to the ICC should be a measure of last resort, which means it can only be done when all national legal instruments have been exhausted.
"It is therefore highly unlikely that this matter will end up in the ICC. The question is whether the Iranian or Iraqi courts will be able to exercise jurisdiction. That is, of course, theoretically possible, although most difficult to foresee this happening, as the US is unlikely to cooperate and would certainly not extradite any of its nationals to either Iran or Iraq to face trial in what would almost certainly be political show trials," the lawyer said.
On Tuesday, Iran’s judicial spokesman, Gholam Hossein Ismaili, said Iran intended to hold the US government and armed forces accountable for the killing of Soleimani and bring the relevant case before the Hague-based court.
On Saturday, Iran's Islamic Revolutionary Guard Corps (IRGC) acknowledged full responsibility for erroneously downing a Ukrainian Boeing 737 over Tehran. The Iranian air defence system had confused the passenger plane with a hostile cruise missile, and due to disrupted communication, the operator single-handedly decided to shoot it down, the IRGC explained.
Iranian President Hassan Rouhani blamed the United States for creating the current political dynamic in the region that had led to the tragedy. The downing of the plane happened on the same day when Iran launched missiles at two bases housing US troops in Iraq in retaliation for Soleimani's assassination.
"What are the consequences for the United States now? Regrettably, very little. There may be diplomatic isolation. There will be harsh words in the UN. There may be renewed hostilities in the region. What I consider to be the greatest risk to the United States is its loss of moral high ground," Cadman said, adding that Iran must first review its human rights record if it wanted to seek justice and accountability.
In early January, US President Donald Trump threatened to target Iranian cultural sites — which constitutes a war crime under the Geneva Convention — in the event Iran decided to retaliate against the United States for killing Soleimani. Later, however, he retreated from this threat.
"Should we support a course of conduct that has been described as effectively using war crimes to combat war criminals? Of course, we should not. It would appear, however, that that is precisely what is being proposed when one speaks of disproportionate military attacks and destruction of cultural monuments," Cadman said.