Israel has declared the case closed. The US state department has done its best to duck difficult questions. But leading members of the US Congress are refusing to drop demands for a proper accounting of the death of the Palestinian American journalist, Shireen Abu Akleh, four months ago.

The longest-serving member of the US Senate, Patrick Leahy, recently upped the ante by warning that Israel’s failure to fully explain the Al-Jazeera reporter’s killing could jeopardize America’s huge military aid to the Jewish state under a law he sponsored 25 years ago cutting weapons supplies to countries that abuse human rights.

Nearly half of the Democratic members of the Senate have signed a letter calling into question Israel’s claim that Abu Akleh was accidentally shot by a soldier. The letter suggests she may have been targeted because she was a journalist.

The Biden administration is also facing a flurry of legislative amendments and letters from members of Congress demanding that the state department reveal what it knows about Abu Akleh’s death and that the FBI launch an independent investigation.

Few think there is much prospect of the US actually cutting its $3.8bn a year in military aid to Israel in the near future, but it is politically significant that so many senior Democrats have signed on to publicly challenge Israel, which has frequently been able to count on solid bipartisan support in America.

Although criticism has focused on Abu Akleh’s death, the demands for accountability come as Israeli killings of Palestinians have escalated while Jewish settlers in the West Bank appear to have been given free rein at times to attack Palestinians and take over their land.

Dylan Williams, senior vice-president of policy and strategy at the Washington-based campaign group J Street, which describes itself as “pro-Israel and pro-peace”, said the demands for justice for Abu Akleh reflect broader concerns.

“Members of Congress seem increasingly frustrated that these types of disturbing actions from Israeli forces continue to take place, without facing meaningful pushback or accountability from our government,” he said.

“There’s growing momentum to make clear that Israel must be held to the same important standards as all close US allies, and that our steadfast support for Israel’s security does not and should not preclude our government from also standing up in defense of human rights and international law in the occupied Palestinian territory.”

The powerful American Israel Public Affairs Committee (Aipac), which funds political campaigns against politicians critical of Israel, has lobbied against a US investigation of Abu Akleh’s death.

But Sarah Leah Whitson, director of Democracy for the Arab World Now – an advocacy group founded by the murdered Saudi dissident Jamal Khashoggi to pressure the US government to end support for authoritarian regimes in the Middle East – said that changing American public sentiment about Israel and the Palestinians has made it easier for some politicians to speak out.

“There is an increasing view among the American public that Israel is committing the crime of apartheid, that Palestinians are unjustly victimised by Israel. This has given legislators more space, particularly secure legislators like Patrick Leahy, to say what they actually think,” she said.

“In addition, they have more space on this particular case because Shireen Abu Akleh was a US citizen.”

Israel initially claimed that Abu Akleh was shot by a Palestinian during a military raid on the occupied West Bank city of Jenin in May. Earlier this month, it finally admitted that it was “highly probable” that an Israel Defence Forces (IDF) soldier killed the journalist but claimed the shooting occurred during a gun battle with Palestinian fighters.

That account was widely dismissed because investigations by human rights groups, the press and the United Nations showed that there was no fighting in Abu Akleh’s vicinity.

Last week, Leahy told the Senate that the Biden administration had failed to act on calls from members of Congress for the FBI to investigate Abu Akleh’s death as is “customary and appropriate after a tragedy like this involving a prominent American killed overseas under questionable circumstances”.

“Unfortunately, there has been no independent, credible investigation,” he said.Leahy challenged the value of Israel’s report on Abu Akleh’s death, noting there was “a history of investigations of shootings by IDF soldiers that rarely result in accountability”.

The senator also questioned the state department’s role after the US security coordinator (USSC) in Jerusalem, Lt Gen Mark Schwartz, concluded that there was “no evidence to indicate [Abu Akleh’s] killing was intentional”.

Leahy said: “The USSC, echoing the conclusion of the IDF, apparently did not interview any of the IDF soldiers or any other witnesses. To say that fatally shooting an unarmed person, and in this case one with ‘press’ written in bold letters on her clothing, was not intentional, without providing any evidence to support that conclusion, calls into question the state department’s commitment to an independent, credible investigation and to ‘follow the facts’.”

Leahy has introduced an amendment, along with other senators, calling for the Biden administration to examine whether Israel has fallen afoul of the 1997 “Leahy Law” barring military assistance to countries whose armies abuse human rights.

“Whether [Abu Akleh’s] killing was intentional, reckless or a tragic mistake, there must be accountability. And if it was intentional, and if no one is held accountable, then the Leahy Law must be applied,” Leahy said.

Senator Chris Murphy, chair of the Senate foreign relations subcommittee responsible for the region, told MSNBC that he had not previously supported calls to set conditions for US military aid to Israel but that he was concerned about its conduct in the West Bank.

“Some of [Israel’s] recent decisions are making conflict between Israel and the Palestinians more likely, not less likely,” he said. “I haven’t gotten there yet, arguing for conditions on that aid, but I think all of us are watching the behavior of the Israeli government very carefully.”

Leahy is backed by other senators including Chris Van Hollen, who pushed an amendment passed by the Senate foreign relations committee earlier this month requiring the state department to hand over a full copy of the USSC’s controversial report on Akleh’s death after the US secretary of state, Antony Blinken, failed to respond to an earlier request and a series of questions.

“I will continue pressing for full accountability and transparency around the death of Shireen. Anything less is unacceptable,” Van Hollen told the committee.

Van Hollen was also instrumental in a letter in June signed by nearly half of all Democratic members of the Senate demanding “an independent, thorough, and transparent investigation” into her killing. The letter said disturbing comments by an Israeli official suggested she might have been targeted because she was a journalist.

“On the day Shireen Abu Akleh was shot and killed, an Israeli military spokesperson, Ran Kochav, stated that Ms Abu Akleh and her film crew ‘were armed with cameras, if you’ll permit me to say so’,” the letter said.

“We know you agree that journalists must be able to perform their jobs without fear of attack.”