"A big part of that ongoing investigation is to evaluate where he was and what he was doing during his time in Pakistan. Beyond that, I don't want to get into a lot of specifics on that at this point," White House spokesman Robert Gibbs told reporters at his daily press briefing.
Without going into specifics, Gibbs said Justice Department and investigating agencies are actively looking at the time which Shahzad spent in Pakistan.
"He has admitted in the charging documents, in the complaint that he went to terrorist training in Waziristan" New York Police Commissioner Raymond Kelly told the Charlie Rose Show on PBS in an interview.
Kelly also said that a team was dispatched to talk to people in Karachi, where several people have been arrested in connection with the Times Square case.
"There is a link to Pakistan," Kelly said, adding that Shahzad has acknowledged about his bomb-making training in Waziristan.
"My guess is you got policemen on their way to Karachi right now who want to talk to the people there," Kelly said.
He said that family members of Shahzad were still in Pakistan and not coming to the United States.
Meanwhile, the Fox news reported that the Times Square bomb suspect was upset with the drone attacks.
In his last trip to Pakistan, Fox News quoting Pakistani officials said that Shahzad was introduced to Qari Hussain, the Number 3 in the top tier leadership of the Pakistani Taliban.
"Pakistani officials said they obtained their information after arresting a man in Karachi who is believed to be a friend of the 30-year-old Pakistani-American who allegedly tried to set off a car bomb in Times Square Saturday night," the news channel said.
"The friend also confessed to having played a crucial role introducing Shahzad to Hussain, a master homicide bomber trainer in North Waziristan where he learned the art of bomb making," it said.
But there has been no US confirmation about it. The news channel said family members, including his elder brother in Canada, have been identified along with bank accounts, associates, and cell phone numbers.
Some people were being monitored according to ongoing investigation, the channel said.
"Investigators are probing potential links between Shahzad, a naturalised American citizen who spent much of the past year in Pakistan, and the Pakistani Taliban which claimed responsibility for the attempted bombing after it occurred," The Washington Post said.
Authorities are also zeroing on Mohammed Rehan, who was arrested in Karachi from a mosque with known links to Jaish-e-Mohammed (JeM) militant group.
Rehan is the chief of JeM in Peshawar and reported to have travelled with Shahzad to that city last July.
A senior US official said investigators looking into possible links between Shahzad and Pakistani groups had found none, "but that doesn't say there is no connection," the CNN reported.
