Shafiq ur-Rehman, a member of the extremist Sipah-e-Sahaba, was believed to have provided unspecified support to the six masked gunmen who massacred 15 worshippers and one Muslim police guard Sunday at St. Dominic's Church in Behawalpur, according to police superintendent Shahid Nizam Durani.
Durani said ur-Rehman was not believed to have been one of the gunmen. However, he was believed to have sent facsimiles to news media claiming responsibility in the name of a heretofore-unknown group, Lashkar-e-Umar.
Police said Rehman was a messenger and facsimile operator at a clinic in the Punjabi city where the attack occurred.
In several raids, the police have detained about 100 people for questioning, but they insisted that ur-Rehman was a leading suspect.
Witnesses said the gunmen pulled up on motorcycles, raced into the church and fired at the congregation with Kalashnikovs while shouting: "Graveyard of Christians Pakistan and Afghanistan" and "This is just a start." The 16 dead included the minister.
Protestants share the Roman Catholic church for services because they have no sanctuary of their own.
President Pervez Musharraf has ordered stepped-up security at all Christian churches in Pakistan, and both the federal and provincial governments have instructed authorities to place the highest priority on apprehending the gunmen.
"Special arrangements have been made and we hope and are sure no repeat of this incident is going to be allowed," he said.
But he warned, "The communities should not solely depend on government security agencies and should themselves take measures for their security."
He declined to say who was to blame for the killings or if they were linked to the U.S. action in Afghanistan, but said there were those who wanted Pakistan to end its support for the U.S. campaign.
"There are parties interested against Pakistan who would like to create fear in the minds of the people not to go ahead fully to win the campaign against terrorists," he said.
Pakistan is 97 percent Muslim. Christians constitute a small portion of the remaining 3 percent.
An elderly woman who survived the massacre says she's received a phone call warning her to "get ready for death."
The 70-year-old witness has been helping police make sketches of the men who sprayed a worship service with automatic weapons fire.
She says a man who identified himself was one of the attackers sounded furious as he told her, "I had spared the old lady on Sunday, but now she will die. Get ready for death."
The woman says the caller also threatened to kill all of her children.
On Tuesday police said they had arrested 13 Islamic militants in connection with the killings.
"We are sure we will break the network of terrorists," Arif Ikram, senior superintendent of the Baawalpur police, told Reuters.
He declined to give details of those detained or the charges they faced, but said more arrests could follow.
The arrests were believed to have been made around Bahawalpur, in Punjab province, local officials said.
Christians have long said they feared becoming targets if unrest broke out in Muslim Pakistan over opposition to the U.S. military action against Afghanistan's ruling Taliban.
Pakistan has been a crucial ally of the United States in its bombing campaign against Afghanistan but its military government is under pressure from hard-line Islamic groups sympathetic to the Taliban.
U.S.-led forces launched air strikes against Afghanistan earlier this month to punish the ruling Taliban for sheltering Osama bin Laden, prime suspect in the Sept. 11 hijacked airliner attacks on the United States, and his al Qaeda network.
Services for those slain took place Monday morning; police had not yet released the victims' bodies. Just before the services, more than 1,500 people streamed past the church's stone gate to mourn. Inside, women wailed and cried, making no attempt to hide emotions. Others cursed the assailants.
"I saw some attackers escaping. I couldn't recognize them," said Aina Bakshi, who was near the church when the gunfire began. "I saw small children crying; some of them were bleeding."
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