The blast at Gaza City’s al-Ahli Arab Hospital’s parking lot on Oct. 17, 2023, has become a flash point in the ongoing war between Israel and Hamas.

While Israel denies any responsibility for the explosion and disputes the number of people killed in the blast, Hamas continues to fault Israel for the explosion, which it says killed about 471 people.

U.S., British and French intelligence have said that the group Palestinian Islamic Jihad likely launched a rocket from Gaza that caused the explosion.

Independent experts have not examined the physical scene outside the hospital to determine what actually happened, and media outlets like The Washington Post and Al Jazeera have relied primarily on available videos to conduct their analyses. Hamas, meanwhile, says that the explosion site has already been cleared of any munition.

We spoke with Stefan Schmitt, a forensic scientist at Florida International University who has investigated war crimes and mass grave sites in multiple conflicts, to better understand what is involved with investigating an explosion site like the one outside the Gaza hospital.

1. What are the major challenges with conducting an investigation like this?

Ideally speaking, you would have some sort of independent group of experts who are not part of the conflict going in to examine the explosion site. These people would have a record of independent reporting that the international community and the public, in general, would accept as credible.

Generally, you want a law enforcement agency to control people’s access to a crime scene like this and who officially records who goes into an out of this area. If that doesn’t happen, as is the case now in the Gaza Strip, then anyone has access to it and there is no way to scrutinize whether evidence has been tampered with or manipulated.

We would be looking for remnants of munition at the site and other things like blast patterns that can help tell you where the weapon came from.

The people investigating something like this would be weapons specialists and forensic experts on conflict-related wounds, such as military physicians with a demonstrated experience in battlefield wounds. Sometimes, by looking at people’s injury patterns, they can understand the type of weapons used.

But in a conflict situation, it’s very rare that anybody with credibility quickly gets to a site like that to investigate it, if ever. It could take years before that happens.

2. What other kinds of evidence are available when a site has been cleared?

A damaged site can still be analyzed, as long as both the places and the victims involved are representative of what actually occurred, and can be verified as real places and people.

Here’s what I mean by that: An investigator would want access to a big enough area of the site, or a certain number of victims that are representative of the overall population affected. One wall with blast or burn marks, or one victim, would not be enough to make conclusions on patterns.

When there is not a lot of physical evidence available at a site, we are left with corroborating and verifying things such as social media videos, witness statements, photographs of victims or craters, etc. Then, though, each one of these need to be verified using a chain of custody process to make sure they actually show what they appear to.

An investigator would also want to analyze things that aren’t easily manipulated or tampered with.

So, just like blood spatter can be analyzed, so too can shrapnel or an explosive pattern. Patterns such as injuries on victims, or things like shrapnel, crater damage and burn pattern still tell us much about the type of weaponry used. Injury and blast patterns over a group of people or a damaged site aren’t easily manufactured or faked.

The lack of an easy path to the truth in situations like these leaves you frustrated. It is nearly impossible to conclude one way or another, and everything is left to making a choice based on faith and limited information.

3. How does disinformation make it harder to independently determine what happened here?

In this particular case, there’s an ongoing conflict and disinformation campaigns on both sides. There’s good reason to be skeptical about anything that comes out of this milieu. So then the question becomes: Who made this publicly available video and can it be corroborated by other independent videos?

The same goes for witnesses and victims – are they identifiable people who were at the scene and not simply photographs of people from another conflict altogether? Is a witness or victim shown on CNN or Al Jazeera a real victim, or is it someone staging a prepared statement for whatever political gain? Verifying and corroborating such information often requires independent, credible experts having access to witnesses and scenes of a crime.

Much of my career, I’ve mobilized forensic scientists to engage in international cases where access is often restricted. An example how this is done in situations where there is no independent access to the scene or witnesses is the BBC’s Verify Team report, which looked at available photographic and video evidence of the damage following the explosion outside the Gaza hospital and asked a series of reputable independent experts for their analysis. The article highlights that it isn’t possible to come to a factual conclusion one way or the other without giving independent investigators access to the site, as well as to witnesses of the incident.

The lack of a path to the truth in situations like these leaves the spectator frustrated, as it is all but impossible to forensically conclude one way or another and everything is left to making a personal choice on what to believe. This doesn’t mean, though, that one is left unable to make decisions based on the available information.

There is one principle in international humanitarian law that lends itself to making a choice in matters like this. This is called the proportionality principle. As individuals, we can decide on whether the military actions taken by one side or another are proportional, within our own definitions of what we believe is morally defensible.

Stefan Schmitt does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.