The suspect in the Times Square car bombing attempt is the latest in a series of U.S. citizens and green card holders to be implicated in a terror plot inside the United States, raising questions about the naturalization process that turns foreigners into Americans.
Several hurdles are in place for immigrants to attain U.S. citizenship and, in turn, its platinum-status passport. Pakistani-born suspect Faisal Shahzad passed through his security checks and became a U.S. citizen in April 2009. He first entered the United States on a student visa in the late 1990s, was granted a special work visa a few years later and obtained a green card in 2006 after his wife, an apparent U.S. citizen, petitioned on his behalf.
An official with U.S. Citizenship and Immigration Services said "it's too early" to say whether any signs were missed in Shahzad's naturalization process. But the official acknowledged that any screening is just "a snapshot in time" and can't catch everything.
"This is just one of those realities that we face," the official said.
While the citizenship process is rigorous and takes about four months, there are areas it can miss.
Take foreign travel.
The main citizenship form asks applicants for a five-year history of their travel outside the United States. It also asks a series of questions about the applicant's criminal and personal background, including whether they have ever been a member of a terror group; ever advocated for the overthrow of any government by force; ever been a part of the Nazi government; ever been a prostitute; ever been "a habitual drunkard"; ever been a polygamist; ever committed a crime but not arrested; or ever lied to get into the United States.
These questions rely a lot on the individual's honesty -- terrorists applying for citizenship probably won't check the box declaring their outlaw affiliations. Similarly, if they've lied to get into the United States before, they are unlikely to admit it during the naturalization process.
A series of background checks, which apply to everyone, is meant to catch the liars. But while travel records may come up in the process, the immigration official said the process does not look in depth at foreign or domestic travel.
"It's just not something that we need to know a lot about," the official said.
The purpose of these reviews, rather, is to check for criminal background -- arrest records, outstanding warrants, criminal records of associates. Names are run through a thorough FBI and Interagency Border Inspection System background check. Fingerprints are also checked by the FBI to establish a possible criminal history.
But as thorough as the process is, the background checks cease once an individual gets his or her citizenship. Citizenship is not generally contingent on good behavior.
Officials say that after the suspect in the Times Square case became a citizen, he traveled to his native Pakistan. Charging documents say he admitted to recently receiving bomb-making training in the country. Another suspect in the case was also arrested in Karachi, Fox News has learned.
"If you get somebody inside the wires, they would say in the military ... if you can keep somebody below the radar screen, allow them to operate without suspicion, they can get into Times Square with a van filled with explosives," he said.
Rep. Charlie Dent, R-Pa., said Tuesday that in light of the Times Square plot, "naturalization and the process we use to vet people probably does need to be looked at," though he said the threat of "homegrown radicalization" is the main concern at this point.
Sen. Joseph Lieberman, I-Conn., told Fox News that it would be going too far to re-examine naturalized U.S. citizens from select countries like Pakistan in light of this incident.
"I wouldn't want to single out a group," he said, calling the majority of citizens of Pakistani descent "totally loyal to our country." But he said an "old law" that allows the U.S. government to strip somebody of his or her citizenship if he is found fighting with an enemy military force should be amended to cover people found to be affiliated with foreign terror groups.
Najibullah Zazi, a Colorado shuttle driver and Afghan citizen, also was able to clear the immigration process and become a permanent U.S. resident. He pleaded guilty in a plot to bomb the New York subway system in February.
For those who come from outside the United States, the naturalization process is complicated and lengthy.
Applicants generally need a sponsor -- a relative, spouse or employer -- to get the green card. Then they have to wait between three and five years to qualify for citizenship.
The citizenship process includes not just background checks, but a citizenship test and final interview. The interview officer has the authority to reject the applicant at the end of the process or send him or her back for further review.