The White House said it was "outraged" Thursday after Pakistan's top court upheld the acquittal and ordered the release of the militant convicted of masterminding the 2002 beheading of US journalist Daniel Pearl.
Joe Biden's administration is "outraged by the Pakistani Supreme Court's decision," his chief spokeswoman Jen Psaki told reporters, underscoring the uneasy alliance between Washington and Islamabad, which has fractured many times over Islamist militancy.
She called the ruling "an affront to terrorism victims everywhere" and demanded the Pakistani government "review its legal options."
The White House statement came after Pakistan's Supreme Court upheld the acquittal of Ahmed Omar Saeed Sheikh, who had been convicted of masterminding the brutal murder of Pearl, the South Asia bureau chief for the Wall Street Journal, by jihadists.
Pearl's killing -- which was filmed -- caused international shock and outrage.
"The court has come out to say that there is no offense that he (Sheikh) has committed in this case," Mahmood Sheikh, who represented the accused, told AFP.
A court order said that Sheikh along with three accomplices connected to the case should "be released forthwith," though it was not clear when that would happen.
Pearl was researching a story about Islamist militants when he was abducted in the southern port megacity of Karachi in Sindh province in January 2002.
Nearly a month later, after a string of ransom demands, a graphic video showing his decapitation was given to officials.
Sheikh, a British-born jihadist who once studied at the London School of Economics and had been involved in previous kidnappings of foreigners, was arrested days after Pearl's abduction.
He was later sentenced to death by hanging after telling a Karachi court that Pearl had already been killed days before the gruesome video of the journalist's beheading had been released.
Pearl's family on Thursday called the decision to free him "a travesty of justice" and pleaded for US intervention in the case.
"The release of these killers put in danger journalists everywhere and the people of Pakistan. We urge the US government to take all necessary actions under the law to correct this injustice," the family said in a statement.
Reporters Without Borders also slammed the ruling, saying that it "will remain as a symbol of the absolute impunity surrounding crimes of violence against journalists in this country."
The ruling follows an outcry last year when a lower court acquitted the 47-year-old Sheikh of murder and reduced his conviction to a lesser charge of kidnapping -- overturning his death sentence and ordering him freed after almost two decades in prison.
That sparked a series of petitions, including from Pearl's family, but the Supreme Court rejected them in the split decision Thursday, upholding the acquittal.
For years Sheikh had denied personally killing Pearl, but the top court heard earlier this week that he had admitted in a handwritten letter from 2019 that was sent to a provincial court to having had a "minor role" .
Lawyers for Pearl's family have argued that Sheikh played a crucial role in organizing the abduction and detention of the journalist, before ordering his captors to kill him.
Defense lawyers, however, say he was a scapegoat and sentenced on insufficient evidence.
Sheikh and the three other men have been held under emergency orders by the Sindh provincial government, which says they are a danger to the public.
Late Thursday the Sindh government said it would file a review petition against the Supreme Court verdict.
It was not clear how long that might take, but Pakistan's attorney general said in a statement that the federal government "is extending full support" to the provincial government in the matter.
Last month the then-US acting Attorney General Jeffrey Rosen said Washington "stands ready to take custody of Omar Sheikh to stand trial here."
Psaki on Thursday said the United States recognizes "past Pakistani actions to try to hold Mr Pearl's murderers accountable and we do note that as of right now Omar Sheikh remains in detention."
"We call on the Pakistani government to expeditiously review its legal options, including allowing the United States to prosecute Sheikh for the brutal murder of an American citizen and journalist."
In January 2011, following an investigation into the killing, a report released by the Pearl Project at Georgetown University made chilling revelations, claiming that the wrong men were convicted for Pearl's murder.
The investigation claimed the reporter was murdered by Khalid Sheikh Mohammed, the alleged mastermind of the September 11, 2001 attacks.
The report also provided granular details about Sheikh's alleged role in orchestrating the kidnapping of Pearl.