"We've now developed evidence that shows that the Pakistani Taliban was behind the attack," US Attorney General Eric Holder told ABC television's Sunday current affairs talk show "This Week."
"We know that they (Pakistani Taliban) helped facilitate it. We know that they probably helped finance it, and that he (Shahzad) was working at their direction," he added.
Shahzad was arrested by the FBI on Monday, May 3, for trying to detonate the car bomb in New York on late Saturday, May 1, evening.
FBI said that Shahzad has confessed to attending a terrorist training camp in Pakistan's Waziristan tribal region.
Speaking about the progess in the case, Holder said that they have been able to get relevant information within a short period of time.
"I think the investigation is proceeding at a good pace. We have developed, I think, a good amount of information in a relatively short period of time, but we will be continuing to work on it," Holder said.
He added that the Times Square incident has made US realised that Pakistani Taliban has both the aim and the capability to attack the country.
"I'm not sure that we didn't think they had that ability. We didn't think that necessarily was their aim. We certainly have seen with the Shahzad incident that they have not only the aim, but the capability of doing that.
"And that's why they have taken on, I think, a new significance in our anti-terror fight," he said.