To his students, Ahmad al-Khatib was a deputy principal at an elementary school in Gaza run by the United Nations agency for Palestinian refugees. To Hamas’s military wing, documents say, he was something else entirely: an infantryman operating out of the southern Gaza city of Khan Younis.

The military wing, known as the Qassam Brigades, kept meticulous records of its fighters, tracking the weapons they were issued and regularly evaluating everything from their fitness to their loyalty. Mr. al-Khatib, an employee of the U.N. agency since 2013, was among them: Secret internal Hamas documents shared with The New York Times by the Israeli government say that he held the rank of squad commander, was an expert in ground combat and had been given at least a dozen weapons, including a Kalashnikov and hand grenades.

The refugee agency, known as UNRWA, operated schools across Gaza before they were shuttered in the wake of Hamas’s Oct. 7 attack on Israel and the ensuing war. The agency, which employs roughly 13,000 people, including thousands in the schools, has a duty to maintain the neutrality of its facilities in the conflict zones in which it operates, including by keeping militants off its premises and payrolls.

But interviews and an analysis of the records shared with The Times by the Israeli military and foreign ministry indicate that Mr. al-Khatib was one of at least 24 people employed by UNRWA — in 24 different schools — who were members of Hamas or Islamic Jihad, another militant group. Before the war, the agency was responsible for a total of 288 schools, housed in 200 different building compounds, in Gaza.