Islamabad, Pakistan ? The killers of Wall Street Journal reporter Daniel Pearl never intended to free him, investigators said Saturday. Pakistani authorities have warned foreign organizations in the country to take precautions, saying the Pearl case may be part of a wider terrorist scheme.

Meanwhile, the man who delivered a grisly videotape confirming Pearl’s murder was being held for questioning in the southern port city of Karachi, Interior Ministry officials in the capital, Islamabad, said on condition of anonymity.

Also Saturday, officials said they have tightened security at a Karachi detention center holding three suspects charged with sending e-mails announcing Pearl’s Jan. 23 kidnapping. The move follows intelligence reports warning that Pearl’s kidnappers may target the suspects because they are witnesses, said two intelligence officials in Karachi.

Pakistani authorities believe Pearl’s murder may be part of a larger terrorist scheme to destabilize the country following President Pervez Musharraf’s Jan. 12 pledge to rid Pakistan of Muslim extremism in the wake of the Sept. 11 terrorist attacks.

The government warned foreign missions, embassies and dignitaries to boost their security, the Interior Ministry officials said, adding that attacks on U.S. interests in Pakistan cannot be ruled out.

On Friday, President Musharraf vowed to deal with terrorists with “an iron hand.” There was an outpouring of condolences and expressions of outrage from Pakistani government officials, journalists, Cabinet ministers and even some Islamic militant groups.

Four key suspects remain at large and Pearl’s body has not been found. It is also unclear exactly when and where he was killed.

An intelligence official said that unless the remaining suspects are apprehended, “it will not be easy to find the remains of the slain journalist.”

The official, who spoke on condition of anonymity, said an Arab national police believe helped coordinate Pearl’s abduction is among those being sought. He did not elaborate.

The alleged mastermind behind Pearl’s abduction, British-born militant Ahmed Omar Saeed Sheikh, has been in custody since early February. Authorities in Karachi said they continued questioning Saeed and the three suspected e-mailers for clues about the location of Pearl’s body and the remaining suspects.

Two intelligence officials in Karachi, speaking on the condition of anonymity, said Saeed told interrogators that his group wanted to teach a lesson to the U.S.-led anti-terror coalition and that Pearl’s murder was just a first step.

The officials said they had been optimistic about Pearl’s safe recovery until the last moment, but that it now seems the extremists had kidnapped him for the purpose of killing him.

Saeed told authorities late Friday that he was not present when Pearl was killed, a senior Karachi police official said. The official also confirmed that Saeed said his group wanted to take more steps to “teach a lesson to America.”

A videotape received by the U.S. Consulate in Karachi “contained scenes showing Mr. Pearl in captivity and scenes of his murder by the kidnappers,” said Mukhtar Ahmad Sheikh, an official in charge of police in Sindh province, which includes Karachi.

A Pakistani investigator told The Associated Press that kidnappers killed Pearl by cutting his throat, and then decapitated him. Speaking on condition of anonymity, he said the kidnappers made two videotapes, one longer than the other, that contained graphic images of Pearl’s death and the moments afterward. Another source close to the investigation said a tape showed Pearl before he was killed saying into the videocamera, “I am a Jew, my mother is a Jew.”

The video footage was obtained by a Karachi-based Pakistani journalist who works for a New York newspaper, Interior Minister Moinuddin Haider told reporters Friday. He did not elaborate except to say the tape was then made available to the U.S. Consul General.

A source close to the investigation told the AP that the person who obtained the tape was not a journalist but rather someone who was “posing as a journalist.”

The Interior Ministry officials said the man who delivered the tape was being held for questioning in Karachi.

“We want to know why the man who posed himself as a journalist had not contacted his own government and the police and what was the purpose of delivering this videotape to the U.S. Consulate so secretly,” one of the officials said.

In a statement Friday, Pearl’s widow, Mariane, who is seven months pregnant, said her husband’s killers could not defeat his spirit and that she would tell their son that his father had worked to end terrorism.

Thanking “all of the people throughout the world who have given Danny and me support and encouragement,” she said the struggle against terrorism was everyone’s responsibility.

Many Pakistanis believe the crime was staged because of Musharraf’s decision last year to back the United States in the war in neighboring Afghanistan, reversing Pakistan’s previous support for the Taliban regime.

Police searched Friday in Punjab province for Amjad Faruqi, who is believed to have carried out the kidnapping.

With Pearl dead, authorities will feel free to go after the killers with all their might, said Jamil Yousuf, a Karachi businessman who heads a citizen-police liaison committee involved in the investigation.

“We were moving very cautiously earlier as the recovery of Daniel Pearl was our prime objective. Now with his death our entire focus is on arresting the key suspects who are believed to have carried out the kidnapping,” he said.

The 38-year-old reporter was kidnapped in Karachi while researching links between Pakistani extremists and Richard C. Reid, who was arrested in December on a Paris-Miami flight he allegedly boarded with explosives in his sneakers.