The April 15, 2013, Boston Marathon bombing that killed 3 people and wounded 264 could generate renewed interest in terrorist watchlist screening and background checks for firearms, because at least one of the alleged perpetrators was reportedly watch-listed as a suspected terrorist. And, on April 18, 2013, the alleged bombers—brothers Tamerlan and Dzhokhar Tsarnaev—are also alleged to have shot a police officer to death, high-jacked an automobile and taken its driver hostage at gunpoint, and engaged in a subsequent shootout with police. According to press accounts, in March and September 2011, the Russian Federal Security Service (FSB, or Federal'naya Sluzhba Bezopasnosti) contacted the Federal Bureau of Investigation (FBI) and Central Intelligence Agency (CIA), respectively, with information that suggested that Tamerlan Tsarnaev (the older brother) had become an Islamic extremist in the past year and intended to travel to Russia to meet with like-minded extremists. While neither the FBI nor CIA reportedly found that Tsarnaev was "radicalized," based on a reasonable suspicion, records on him were possibly included in several border and aviation screening systems. These systems reportedly included an FBI record in a file on "persons of interest," who might engage in "suspicious travel," in the Department of Homeland Security's (DHS's) TECS; and a file based upon a CIA nomination to the National Counter Terrorism Center's Terrorist Identities Datamart Environment (TIDE), which was subsequently the basis of a terrorist watchlist record placed in the FBI-administered Terrorist Screening Center's Terrorist Screening Database (TSDB). Both the TIDE and TSDB are described in greater detail below. However, Tamerlan Tsarnaev's name was possibly spelled or transliterated differently from the Cyrillic alphabet, or even misspelt, on the watchlists in TECS and the TSDB, or on the passenger flight manifests submitted to DHS for pre-flight screening; as a possible consequence, potential watchlist matches were not made and authorities were not fully alerted about his travels to Russia from January through July 2012. Critics claim that had those officials been more fully alerted to his travels, they might have been prompted to more carefully scrutinize his behavior prior to the bombing. In addition, on April 18, 2013, the Tsarnaev brothers allegedly shot and killed a Massachusetts Institute of Technology campus police officer, in an attempt possibly to seize that police officer's firearms. The brothers were reportedly armed with a 9mm Ruger semiautomatic pistol, when they attacked this police officer. This pistol was reportedly recovered at the scene of the subsequent shootout with police, and the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) is tracing this pistol. Prior to the shooting, attempts had been made to obliterate the pistol's serial number, but authorities managed to raise all nine digits of its number. This tracing process may provide information about how the brother(s) acquired the firearm. If the older brother, Tamerlan, had acquired the firearm from a federally licensed gun dealer, then the federally required background check may have triggered a terrorist watchlist hit that, in turn, would have possibly prompted authorities—particularly the FBI-led Boston Joint Terrorism Task Force—to reopen a preliminary assessment that it had previously conducted on him based upon the March 2011 Russian FSB tip and apparently closed in June 2011. The Boston JTTF, moreover, may have found cause to deny the firearms transfer to him. The Administration is reportedly conducting a top-to-bottom review to make sure that intelligence on the bombing was not missed, and Members of Congress have called for hearings. In the 113 th Congress, even before the Boston bombing, Senator Frank Lautenberg and Representative Peter King had reintroduced their similar, but not identical, bills, the Denying Firearms and Explosives to Dangerous Terrorist Act of 2013 ( S. 34 and H.R. 720 ), known to supporters as the "Terror Gap" proposal. Also, in April 2013 when the Senate considered the Safe Communities, Safe Schools Act of 2013 ( S. 649 ), Senator Lautenberg filed an amendment ( S.Amdt. 734 ) to this bill that is similar, but not identical, to his Terror Gap proposal ( S. 34 ). While the Senate leadership has set S. 649 aside, if the Senate reconsiders this bill, it might also consider S.Amdt. 734 . In the wake of Boston, Senator Lautenberg has called for Congress to consider his bill to close the "Terror Gap." In addition, Representative James Moran has included similar provisions in the NRA Members' Gun Safety Act of 2013 ( H.R. 21 ). Following the September 11, 2001, terrorist attacks (9/11 attacks), the George W. Bush Administration took measures to consolidate and expand the use of terrorist watchlists maintained by the federal government. As part of this process, the Department of Justice (DOJ) directed the FBI to modify their firearms- and explosives-related background check procedures to screen prospective firearms buyers and state-issued permit applicants (Brady background checks), as well as explosives license and permit applicants, against terrorist watchlist records. Those modified procedures became effective in February 2004. In addition, under the modified procedures FBI counterterrorism agents found it useful and arguably prudent to maintain and share information about terrorist watchlist-related matches for approved firearms transfer records. However, a provision of federal firearms law requires that all approved firearms transfer records held by the National Instant Criminal Background Checks System (NICS), including those related to terrorist watchlist matches, be destroyed within 24 hours. While the Attorney General has no specific statutory authority to screen those buyers and applicants against the terrorist watchlist records nor maintain records on approved firearms transfers for longer than 24 hours, the modified background check procedures initially generated little public outcry from opponents of greater federal gun control. At the same time, several Members of Congress raised public safety concerns about the possibility that terrorists might exploit the general availability of firearms in the United States. They tasked the Government Accountability Office (GAO) with evaluating the modified Brady background check procedures for firearms and, later, background check procedures for explosives. Since then, GAO has reported on several occasions that subjects of positive terrorist watchlist hits were transferred firearms and, less frequently, explosives. Over nearly 7 years (2004-2010), 1,453 federal firearms-related background checks resulted in terrorist watchlist matches; 1,321 (90.9%) were allowed to proceed. Those transfers were allowed to proceed because being on a terrorist watchlist is not, in and of itself, a disqualifying factor under either federal firearms or explosives law. GAO's confirmation that firearms have been transferred from federally licensed gun dealers to individuals watch-listed as known or suspected terrorists has lent impetus to a legislative proposal that was originally developed by DOJ, under Attorney General Alberto Gonzales, and submitted to Congress in April 2007. This proposal would give the Attorney General discretionary authority to deny firearms or explosives transfers to any watch-listed individuals if he deemed them to be "dangerous terrorists." In the 110 th Congress, Senator Lautenberg and Representative King introduced this proposal as the Denying Firearms and Explosives to Dangerous Terrorists Act of 2007 ( S. 1237 / H.R. 2074 ). Supporters later dubbed this bill the "Terror Gap" proposal. In the 111 th Congress, the November 2009 Fort Hood shooting renewed interest in this proposal, which Senator Lautenberg and Representative King had previously reintroduced ( S. 1317 / H.R. 2159 ). In May 2010, the Senate Homeland Security and Governmental Affairs Committee (HSGAC) held a hearing on "terrorists and guns" and debated the need to pass legislation like the Terror Gap proposal. While no further action was taken on the bill, Senator Lautenberg and Representative King reintroduced the Terror Gap proposal ( S. 34 and H.R. 1506 ) in the 112 th Congress. This report examines potential policy issues that could arise under the Terror Gap proposal. For context, a basic overview of the U.S. government's post-9/11 terrorist watchlist procedures is provided, as well as an analysis of the Terror Gap proposal, which has been reintroduced in the 113 th Congress ( S. 34 and H.R. 720 ). Possible issues could include the following: Should U.S. persons—citizens and legal permanent residents—be notified when the Attorney General makes a "dangerous terrorist" determination about them for the purposes of gun control following a terrorist watchlist match? What form of redress and remedy would be provided for misidentifications, improper watch-listing, and wrongful denial? If enacted, moreover, would these redress and remedy provisions serve as a precedent for other terrorist screening procedures for which Congress has not provided similar avenues of relief? Would the Terror Gap proposal draw unwanted public attention to terrorist watchlists and related screening procedures, possibly undermining the effectiveness of those measures by making terrorists and other adversaries aware of them, and possibly setting a judicial review precedent for other terrorist watchlist screening processes? As noted above, the Terror Gap proposal would grant the Attorney General the authority to deny firearms transfers and state-issued firearms permits, as well as federal licenses to deal in firearms, to watchlisted persons if he deemed them to be "dangerous terrorists." The proposal would also grant the Attorney General similar authority to deny federal licenses to deal in explosives or federal permits to handle explosives.