LONDON — MI5 faced new questions last night over its failure to prevent the July 7 bombings as it emerged that two of the suicide attackers were in their sights more than a year before the atrocity.

The disclosures followed the conviction yesterday of five British Muslim members of a Qaeda gang who plotted to blow up a nightclub, shopping centers, and utilities with home-made fertilizer bombs. The intelligence services were also facing questions about how:

• MI5 followed Khan to his mother-in-law’s home in Dewsbury and established that it was his car in which Mr. Khyam occasionally traveled. But Mr. Khan’s name was never confirmed and he was dismissed as a peripheral figure.

• They failed to alert West Yorkshire Special Branch, show them his photograph or pass on his car number plate details.

• Messrs. Khan and Khyam both attended a terror training camp together in Pakistan two years before the July 7 attacks on London’s transport system, which killed 56 people, including the four terrorists. Their contact was a man called Mohammed Quayam Khan, known as Q, who was under surveillance by MI5 for allegedly providing funds, equipment and recruits to Al Qaeda. Mr. Khan had been in mobile phone contact with Q.

At the Old Bailey yesterday, the five Muslims were found guilty of conspiracy to cause explosions after the longest terrorist trial in the country’s history. Two others were acquitted. The jury had deliberated for 27 days.