In one sense, Shahzad was a lone wolf, with evidence suggesting that he alone bought, assembled, and delivered his botched IED. But, sources say it's also clear Shahzad had some help, drawing inspiration, financial support and bomb training from the Pakistani Taliban.
"It demonstrates that there is a foreign power nexus to this plot, that this wasn't some random individual acting on his own," said CBS News national security analyst Juan Zarate.
CIA chief Leon Panetta and National Security Advisor Jim Jones have provided Pakistani officials with - what sources say - is compelling evidence linking Shahzad with the Taliban, including a "detailed file of Shahzad's contacts" and names, addresses and phone numbers of people Shahzad met with in Pakistan.
Special Section: Terrorism in the U.S.
Authorities there have rounded up 15 to 20 people including a friend who allegedly introduced Shahzad to militants, the son of a caterer who's done business with the U.S. Embassy, and a retired Pakistani Army Major who may have had phone contact with Shahzad.
But, none has been conclusively linked to the attack and many, including the Army Major, have now been released.
Here in the United States, the FBI continues chasing thousands of leads, digging through cell phones, computers and files seized in recent raids.
But, the investigation has turned up no co-conspirators. Three men, arrested on immigration charges, apparently helped Shahzad import money from Pakistan, but sources say they had no knowledge of his plot.
Shahzad's attack has been labeled amateurish. But former CIA analyst Phil Mudd says we should take no comfort in that.
"Everybody's an amateur until people die, even people who have limited training and limited access to an al Qaeda trainer - or no access - can kill tens or hundreds," Mudd said.
While there's no indication Shahzad is part of a larger cell, the government warns others like him maybe be in the United States - radicalized Americans with terrorist connections and a desire to strike the homeland.