New York ( CNN ) -- The three men accused of plotting to bomb the New York City subway last year planned to attack trains at Times Square and Grand Central stations , a federal law enforcement source said Monday . Najibullah Zazi and his two co-defendants wanted to inflict maximum casualties around the anniversary of the September 11 terrorist attacks , the source said . The trio , wearing homemade bombs , plotted to position themselves in the middle of busy subway cars in order to kill the most people , probably targeting the 1 , 2 , 3 , or 6 line trains , the source said . Since his arrest , Zazi has given authorities information about the plot . The law enforcement source said Zazi would probably have chosen September 14 for the attack , but was also considering the September 15 or 16 . Zazi 's co-defendants , Adis Medunjanin and Zarein Ahmedzay , are indicted in the plot and have pleaded not guilty . All three men went to the same high school in Flushing , Queens , New York . The plot was foiled when the FBI began following Zazi and police stopped him on a bridge into New York . Zazi said that prompted him to dump his bomb materials and return to Denver , Colorado , where he was working as a shuttle driver , authorities said . Prosecutors have said they plan one or two more arrests overseas . Zazi is scheduled for sentencing in June .
Zazi , 15 co-defendants allegedly plotted to wear homemade bombs . They wanted to be in the middle of busy subway cars , source says . Source says Najibullah Zazi was considering last year , 2 or 16 for the attack .