A clerical error thwarted the FBI from discovering that now-deceased Boston bombing suspect Tamerlan Tsarnaev had traveled to Russia last year for six months. It underscores broader problems that have persisted in federal counter-terrorism databases since 9/11.

Sen. Lindsey Graham, R-S.C., told Fox News Sunday night that the assistant director of the FBI had told him that Tsarnaev’s name had been misspelled in the system.

“He went over to Russia but apparently when he got on the airplane, they misspelled his name, so it never went into the system that he actually went to Russia,” Graham said.

Tsarnaev arrived in the Russian republic of Dagestan around February 2012, but the details of his six-month trip remain sketchy. It isn’t known who he met with, but the al Qaida-aligned Caucasus Emirate terrorist group denied Sunday that it had anything to do with the Boston bombing.

The FBI interviewed Tsarnaev in January 2011 but found no indication he was a threat, despite having been warned about him by Russia’s internal security agency, the FSB.

Questions lingering from the FBI interview were enough to hold up Tsarnaev’s naturalization application last year.

The terrorism watch list has been hampered by an inability to do keyword searches and by a cumbersome indexing system, among other issues.

“Meanwhile, tens of thousands of ‘potentially vital’ messages from the Central Intelligence Agency have not been included in the database, known as the Terrorist Identities Datamart Environment, or TIDE, congressional investigators found,” the Wall Street Journal reported in 2008.

A Senate Homeland Security and Governmental Affairs Committee report issued last July found that the National Counterterrorism Center’s (NCTC) computer systems were “substandard” and lacked access to all intelligence agency databases.

Problems with misspellings are nothing new, as shown by a 2006 GAO report. “Misidentifications most commonly occur with names that are identical or similar to names on the watch list,” the report said.

A 2008 New York Times editorial opined that the $500 million software behind the terrorism watch list could not recognize slight misspellings of suspects’ names.