<p>Washington, Sept. 18 (Bloomberg) -- The FBI is investigating whether terrorists plotted to seize more than the four jetliners commandeered last week for deadly attacks on the World Trade Center and the Pentagon, U.S. Attorney General John Ashcroft said.</p>
<p>The U.S. is broadening the largest criminal investigation in FBI history and is concerned about further attacks, he said. Authorities have detained 75 people on immigration charges, up from 49 as of yesterday, and investigators believe associates of the 19 hijackers may still be in the U.S. The FBI has received more than 96,000 tips, including many that are redundant or contradictory, Ashcroft said.</p>