NEW YORK (CNN) -- A federal grand jury in New York has stepped up its investigation of Osama bin Laden, the elusive millionaire who was the target of Thursday's U.S. missile attacks in Afghanistan and Sudan, CNN has learned.

A federal law enforcement source tells CNN that an Afghani national, Wali Khan Amin Shah, has been providing information about bin Laden, who has been the focus of a grand jury probe for more than a year. However, the source refused to characterize the nature of the information that has been provided by Shah about bin Laden.

Shah has been cooperating with authorities since his 1996 conviction on charges that he was part of a plot to blow up 12 airliners over the Pacific Ocean in 1995.

One of the men convicted with Shah in that plot, Ramzi Yousef, was later tried and convicted of the World Trade Center bombing.

The plan to bomb airlines, called Project Bojinka, was uncovered when a fire broke out in an apartment in Manila, Philippines. Inside, authorities found pipe bombs and computer disks with details of the plot, as well as a plan to kill Pope John Paul II.

During the trials for Shah, Yousef and a third conspirator, Abdul Hakim Murad, no ties were established between the men and bin Laden. However, Yousef was arrested while living in a boarding house in Pakistan that was owned by bin Laden.