An indictment filed in New York on Thursday charges Shahzad with 10 terrorism and weapons charges, adding five counts to the original case against him.
The 30-year-old Shahzad is charged with attempted use of a weapon of mass destruction among several terrorism and weapons charges.
The Pakistan-born U.S. citizen was arrested two days after his smoking SUV was found with a homemade gasoline-and-propane bomb that failed to ignite.
Authorities say he cooperated with investigators for two weeks before he asked for a lawyer.
Shahzad's attorney didn't return a call for comment on Thursday.