Authorities are warning of the danger of a "lone wolf" attack a day ahead of the eleventh anniversary of the Sept. 11 attacks.
So far, however, there have been no warnings for law enforcement across the country to be on high alert.
According to a new law enforcement bulletin, the successful targeting of al Qaeda leaders has led to a decline in threats of a 9/11-style attack from the terrorist group.
"Twenty-three of the top 30 al Qaeda commanders are off the field - either dead or captured in the last two, three to four years. So this has been a pretty tough series of months and years for al Qaeda," Michael Breen, vice president of the Truman National Security Project, said.
While an al Qaeda threat is diminished, officials still fear the possibility of an individual carrying out an attack on their own.
Security officials say lone terrorists, like the man who tried to set off a bomb in New York City's Times Square, can be harder to stop.
"We'll have our standard counter-terrorism overlay. You know, we have a special unit assigned to security of the memorial, so we feel that we're doing everything appropriate to secure it," New York City Police Commissioner Ray Kelly said.