The militant, Qari Abdul Hayee, a leader of the Islamist militant group Lashkar-e-Jhangvi, was arrested by the paramilitary Rangers force on Sunday in Karachi, the city where Mr. Pearl was held hostage and killed.

“We were after him for the past three weeks. We had information he was in Karachi,” said a senior Rangers official, speaking by phone on the condition of anonymity.

Mr. Hayee was arrested on University Road, which runs through several residential neighborhoods and educational institutes. But it was not clear where he was being held.

The Rangers official that the militant had been handed over to the city police’s Crime Investigation Department on Sunday evening. But police sources in Karachi, also speaking on the condition of anonymity, denied that Mr. Hayee was in their custody.

It is not the first time Mr. Hayee has been reported arrested since the death of Mr. Pearl, 38, a reporter for The Wall Street Journal. The militant was arrested in 2003 in Multan, a city in the southern part of Punjab Province, in connection with the death of six Shiites. He was later acquitted and continued to live freely in Punjab Province, where Lashkar-e-Jhangvi has its strongest roots.

Pakistani officials have said the Mr. Hayee and other figures in Lashkar-e-Jhangvi were at least partly involved in Mr. Pearl’s abduction, though not his death. Mr. Hayee’s suspected role has been described as acting as a “facilitator” who had close ties with other men involved in the kidnapping. At the time of his arrest in 2003 in a case related to Shiite killings, which dated back to the 90s, Mr. Hayee was also investigated for his role in Pearl’s murder. It remained unclear what led to his subsequent acquittal.

Mr. Hayee, who also goes by the name of Asadullah, was identified as a weapons and explosives expert for Lashkar-e-Jhangvi Lashkar is Pakistan’s most notorious sectarian militant outfit, and has returned to prominence this year after it claimed responsibility for two devastating bombings in the western city of Quetta that killed about 200 Shiites, mostly from the ethnic Hazara minority.

Mr. Hayee appears to have been arrested as part of a crackdown by the security forces on Lashkar after widespread criticism following the two Quetta bombings and a third attack in Karachi this month, also thought to be the work of Lashkar militants.

Pakistani officials declined to share details of Mr. Hayee’s arrest on Sunday. A private security consultant in Karachi speculated that Mr. Hayee may have been visiting madrasas in the Safari Park neighborhood, which is close to University Road.

Mr. Pearl was abducted in January 2002 in Karachi and beheaded the next month. His killing sent shock waves throughout the world and shed a light on the growing nexus of Al Qaeda and Pakistani militant groups.

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