Here’s the available evidence of what happened at Al Ahli Arab Hospital in Gaza

Video and photographic evidence, along with eyewitness accounts, are providing some clues about Tuesday’s massive explosion at Gaza’s Al Ahli Arab Hospital, which Palestinian officials say killed hundreds.

Hamas blames an Israeli airstrike for the blast, a charge the Israeli Defense Forces have vigorously denied. Israel says that a Palestinian rocket, launched by a Palestinian militant group called Islamic Jihad, exploded in mid-air and fell on the hospital grounds. The U.S. believes Israel is not to blame, based on analysis of “overhead imagery, intercepts and open source information,” a National Security Council spokesperson said Wednesday.

Social media is awash with claims and counterclaims of who was behind the explosion, according to Kolina Koltai, a researcher with the open source investigations group Bellingcat. “Immediately it just became a very confusing situation,” she says. “You have conflicting claims, all this footage.”

Here is what the available evidence shows so far.

Many civilians had taken shelter at the hospital to avoid ongoing airstrikes

There were hundreds of people, including families, who had come to the hospital to hide from the bombardment elsewhere in Gaza, according to Dr. Fadil Naim, the head of the orthopedics department, who was working at the time of the blast. The hospital, Gaza’s oldest, is run by a Christian group.

Israel has conducted thousands of air strikes on Gaza in the twelve days since a wave of attacks by Hamas militants killed more than a thousand Israelis. Church officials and the Palestinian Ministry of Health say that Israeli fire had previously struck the hospital on Oct. 14.

Despite that incident, because the hospital belonged to the church, civilians “thought the hospital was the most safe place in Gaza,” Naim told NPR.

The displaced Palestinians were in a courtyard outside the hospital at the time of the blast. The small courtyard had several parked cars and a few grassy patches where people appear to have congregated.

Eyewitness videos appear to have captured the moment a massive fireball erupted in the courtyard

Sometime in the evening local time, several videos appear to have captured a massive explosion and fireball at the hospital.

Several experts in geolocation have shown that the videos show the blast occurring at the hospital and NPR independently was able to verify those geolocations.

One video, a live broadcast feed from the news channel Al Jazeera, appears to show what could be a rocket launching from a site west of the hospital. The rocket, or other object, appears to break apart high above the hospital moments before the blast.

The Israeli Defense Forces claim that radar data shows a barrage of rockets was launched from an area southwest of the hospital at the time the explosion occurred. While the geometry of the Al Jazeera video aligns with that claim, there is no way to independently confirm the radar data.

Photos and an account of the aftermath provide some clues about the type of explosion that occurred

Dr. Naim was in the hospital’s operating room the moment the explosion occurred, he told NPR. Upon hearing the blast, he rushed outside to find horrific injuries to the people in the courtyard, including amputated limbs and vascular injuries, he said. “Some of them died in our hands,” he said.

Notably, Naim also said that there were no deaths among the hospital’s staff, many of whom were working inside at the time of the explosion. “Luckily none of our staff was killed, but we had two injured,” he says.

Photos from the following day also appear to show little damage to the hospital buildings, and a relatively small blast zone from the explosion. That damage pattern is inconsistent with a large air-dropped bomb, which would leave a crater and create a shockwave that would damage or destroy surrounding structures, says Marc Garlasco, a former targeting officer for the U.S. military who now works for PAX, a Netherlands-based non-profit.

“It’s very clear to me that this is not an airstrike.” Garlasco says. Israeli bombs typically leave craters three to ten meters in size, and are designed to create a large shockwave that propels shrapnel over a large area.

The lack of both shrapnel damage and structural damage to the hospital is inconsistent with all types of commonly used Israeli bombs and artillery shells, he says.

Death estimates vary widely, but are believed to be in the hundreds. Garlasco, who has investigated war crimes all over the world, says such a high death toll would be toward the “extreme high end of anything I’ve ever seen.” But he found it plausible, he said, given that so many Palestinian civilians have left their homes to seek refuge in a small number of supposedly safe locations.

“It really speaks to the issue of Palestinians being packed into areas they believe are safe,” he says.