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As the news broke Wednesday that Pakistani police had arrested the leader of an Islamist militant group blamed for the terrorist attacks that killed 166 people in Mumbai, India, in 2008, President Donald Trump hailed it as a breakthrough for his tough policy toward Pakistan.

“After a ten year search, the so-called ‘mastermind’ of the Mumbai Terror attacks has been arrested in Pakistan,” he declared in a tweet. “Great pressure has been exerted over the last two years to find him!”

But Hafiz Saeed, the leader of the group Lashkar-e-Taiba, was hardly on the run. He is a powerful, high-profile figure who oversees a network of charities, schools, hospitals and other institutions as well as armed militants, and he had recently appeared at political rallies and court hearings.

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During the last decade, Pakistani authorities have detained him at least three times, but he was ultimately released without charges or exonerated by the courts.

Saeed’s past arrests were seen as part of the Pakistani government’s periodic efforts to placate the increasing impatience in Washington with its longtime support of Lashkar and other militant groups. The Trump administration has suspended hundreds of millions of dollars in military aid to Islamabad for its failure to rein in Islamist extremists. On Wednesday, skeptical counterterrorism officials and experts warned that the latest arrest of Saeed could be part of a recurring ritual in which Pakistan detains Lashkar bosses in response to international pressure, then fails to follow through. The critics linked the timing to the impending visit of Imran Khan, Pakistan’s prime minister, to Washington to meet with Trump.

“The U.S. should interpret this as a small step,” said Jason Blazakis, a professor at the Middlebury Institute of International Studies at Monterey and a former senior counterterrorism official at the State Department. “Any conclusion that this is a paradigm shift in Pakistan’s larger treatment of Lashkar is grossly naive. If Pakistan wanted to send a stronger message, they would arrest individuals indicted by the Americans for killing Americans.”

In 2011, U.S. prosecutors charged Lashkar leaders including Sajid Mir, accused of being the operational mastermind of the plot, as well as a Pakistani intelligence officer in the deaths of six Americans in the assault on Mumbai. Pakistan has never arrested Mir, the intelligence officer or other key suspects, despite strong evidence of their involvement and whereabouts and pressure from U.S. law enforcement. Federal prosecutors have not publicly charged Saeed in the case. It could not be learned if prosecutors have filed a sealed indictment naming him.

The fact that Saeed faces charges of terrorist financing and diversion of funds from charities, rather than involvement in the Mumbai attacks, suggests that the Pakistani move is largely symbolic, an Indian police counterterrorism chief said in a telephone interview.

Read More Trump Takes a Tougher Line on Pakistan, but the 2008 Mumbai Attack Goes Unpunished Although the administration’s policy shift has raised hopes, a Pakistani intelligence officer and others indicted in the killings of 166 people remain at large. Critics say the Pakistani government protects them.

“If he is charged in the Mumbai attacks, that could be a reason to believe they are taking a more hardline approach, otherwise I think it is just a drill that is performed at regular intervals,” said Deven Bharti, of the Maharashtra state police. Bharti personally battled the Lashkar gunmen in 2008 and led the subsequent investigation.

Asked for comment Wednesday, a State Department official confirmed that Pakistani authorities had arrested Saeed on terrorism financing charges.

“The United States calls for Saeed’s full and expeditious prosecution for his involvement in the planning of numerous acts of terror, including the 2008 Mumbai attacks that killed 166 innocent people, six Americans among them,” the official said.

At a 2011 trial in federal court, prosecutors introduced detailed evidence linking Pakistan’s powerful Inter-Services Intelligence Directorate, the ISI, to the Mumbai attacks. A confessed Pakistani American operative for the ISI and Lashkar, David Coleman Headley, testified that the ISI had worked closely with the group Saeed founded to carry out the three-day assault by a team of 10 gunmen. Saeed and ISI officers intended from the beginning to kill Americans, Jews and Indians, according to interviews and court documents.

ProPublica has done extensive reporting on Headley, the role of the ISI in terrorism, and the failure of the U.S., British and Indian governments to detect the plot despite high-tech intelligence and repeated warnings from Headley’s family and associates.

In June, Khan promised to get tough with militant groups. The arrest of Saeed came as part of an operation targeting a dozen Lashkar operatives for terrorism financing, according to public statements by Pakistani officials.

But experts see few signs of dramatic change. The trial in Pakistan of half a dozen suspects charged in the Mumbai attacks remains stalled nine years after it began. In interviews, U.S. counterterrorism officials have accused the ISI of allowing the defendants to direct terrorist operations while they were held in comfortable jail conditions. Even if Saeed remains in jail or is placed under house arrest, he will probably retain authority over his group, Blazakis said.

“Saeed is a well-known individual,” Blazakis said. “He’s a guy who has been arrested before. Even when they are behind bars, the track record shows that Laskhar’s leaders continue to be effective.”

By remaining loyal to the Pakistani state, Lashkar has eluded crackdowns and even expanded the presence of its militants in neighboring Afghanistan, where international talks with the Taliban are a U.S. priority, said American University Professor Tricia Bacon, a former State Department intelligence analyst and expert on South Asia. The difficult negotiations with the Taliban to seek peace in Afghanistan are likely to be high on the agenda of Trump’s upcoming meetings with Khan. Because of its deep ties to the Taliban, Pakistan is key to any accord in Afghanistan, and Lashkar can serve as a useful proxy there, Bacon said.

“Lashkar has demonstrated its willingness to play the pawn for the Pakistani state,” Bacon said. “This follows a road map we have seen before. I would be surprised if [Saeed’s arrest] turns into anything significant.”

Saeed has denied involvement in terrorism and claimed that he has distanced himself from Lashkar, which he founded in the late 1980s. Pakistan has denied U.S. and Indian charges that the indicted Pakistani intelligence officer, identified in court as Major Iqbal, and other ISI officials played a role in directing and financing the plot and protecting Lashkar masterminds afterward.

Pakistan’s recent moves against Lashkar also respond to pressure from the Financial Action Task Force, or FATF, an international body that combats terrorism financing and money laundering, experts said. Last year, the FATF put Pakistan on its “gray list” of high-risk nations, finding that the government in Islamabad has not taken sufficient action against illicit funding of militant groups. Pakistani leaders fear the economic consequences of ongoing scrutiny, especially if the international group moves Pakistan to its blacklist of nations that fail to fight financial crime, experts said.