LEEDS, England - Police in Egypt questioned a biochemist about the London subway bombings, trying to decide whether to hand him over to British investigators after authorities in this northern town reportedly found traces of explosives in his bathtub.

In another sign of the investigation's widening global reach, Metropolitan Police Commissioner Sir Ian Blair said authorities were trying to determine whether any of the four "foot soldiers" - the suicide bombers who ranged in age from 18 to 30 - had ties with Pakistan-based cells of the al-Qaida terror network.

In an interview with BBC radio, Blair said the inquiry was focusing on the organizers of the attacks and confirmed police were most interested in the Pakistan connection. The bombings of three subway trains and a bus killed 55 people, including the bombers. Police increased the death toll from 54 on Saturday after another victim died in the hospital overnight.

Three of the bombers - Shahzad Tanweer, Mohammed Sidique Khan and Hasid Hussain - were Britons of Pakistani origin. At least two had traveled to Pakistan.

Two senior Pakistani intelligence officials said Friday that authorities in that country were looking into a possible connection between Tanweer and two al-Qaida-linked militant groups, and specifically a man arrested for a 2002 attack on a church near the U.S. Embassy in Islamabad.

On Saturday, intelligence and school officials said Pakistani authorities questioned several students, teachers and administrators at one of two religious schools - or madrassas - believed visited by Tanweer.

British police on Saturday continued searching a shop called Iqra Learning Centre in the Leeds neighborhood of Beeston. The shop, which officers raided on Friday, appeared to sell Islamic books and DVDs and offer seminars and presentations.

The shop is about four miles from Egyptian chemist Magdy Mahmoud Mustafa el-Nashar's town house, where British news media reported that police found evidence of the explosive TATP inside a bathtub.

TATP was used by shoe bomber Richard Reid, whose attempt to blow up a trans-Atlantic flight from Paris to Miami in December 2001 was thwarted. Reid pleaded guilty to U.S. charges and is serving life in prison.

Egypt's Interior Ministry announced Friday that Egyptian authorities were interrogating el-Nashar, who had studied for one semester at North Carolina State University and the University of Leeds. It said el-Nashar denied having any connection to the attacks.

An Egyptian government official said el-Nashar, 33, was arrested in Cairo on Sunday or Monday after British officials informed Egypt of their interest in him.

In London, Blair said British authorities would seek his extradition, if need be, although the two countries do not have an extradition treaty.