Mr. al-Nasasra was part of a convoy of emergency crews sent by the Red Crescent and Gaza’s Civil Defense, another rescue service, to search for a Red Crescent ambulance that had disappeared earlier in the morning of March 23. Israeli forces had opened fire on that first ambulance, killing two members of its crew and detaining the third, Munther Abed, according to both the Israeli military and Mr. Abed, who was later released.

When the rescue convoy arrived on the scene and paramedics got out to look at the first ambulance, Israeli soldiers began shooting again in a barrage that lasted about five minutes, according to the video of the attack, which was discovered on the cellphone of one of the paramedics who was killed, published by The New York Times and later released by the Red Crescent.

Soldiers found Mr. al-Nasasra alive after firing on the convoy and detained him alongside Mr. Abed, the survivor from the first ambulance, Mr. Abed told The Times in an interview. Two other witnesses who were held with the paramedics — Saeed al-Bardawil, a doctor, and his 12-year-old son, Mohammed, who had been detained as they headed to the beach to fish — confirmed Mr. Abed’s account.

Mr. al-Nasasra was stripped, handcuffed and blindfolded, Mr. Abed and Dr. al-Bardawil recalled.

The two paramedics spoke in whispers about the fate of their colleagues, Mr. Abed said. The Israeli soldiers detaining them later questioned the paramedics, asking them for their names, ages and ID card numbers, and appeared to scan their faces with a device Mr. Abed did not recognize, Mr. Abed said.

At some point, Mr. Abed and Dr. al-Bardawil recalled, Mr. al-Nasasra was taken elsewhere and they had no more contact with him.

In all, Israeli troops killed eight Red Crescent paramedics, six other emergency responders from the Civil Defense, and a United Nations worker who happened to drive by later that morning, according to the Red Crescent and the Civil Defense. Their bodies were not found for days.