Authorities later discovered that Ramzi Yousef , a passenger on the aircraft 's prior flight leg , had placed the explosive . Yousef boarded the flight under the fake Italian name " Armaldo Forlani " , an incorrect spelling of the name of the Italian legislator Arnaldo Forlani . Yousef was later convicted of the 1993 World Trade Center bombing
1993 World Trade Center bombing
1993 World Trade Center bombing
Philippine Airlines Flight 434