The FBI had alerted police in Texas before two gunmen opened fire outside a provocative anti-Muslim cartoon event, according to media reports.
A bulletin was issued to local authorities in Garland, Texas, about Elton Simpson's interest in the May 3 contest for cartoons depicting Prophet Muhammad, three hours before he and Nadir Soofi launched their attack, said CNN, citing FBI Director James Comey's comments at a meeting with reporters in Washington.
Both gunmen were shot dead by police outside the Curtis Culwell Center, where the contest was held.
"I know there are other Elton Simpsons out there," Comey said, according to CNN.
Simpson was sentenced to three years probation in 2011 for lying to federal agents about plans to travel to Somalia to join a terror group in the east African country.
Comey said there had been no indication in the information distributed to Garland police that Simpson was planning an attack, the New York Times said.
The "Muhammad Art Exhibit and Cartoon Contest" was sponsored by the New York-based American Freedom Defense Initiative.
The pro-Israel group led by Pamela Geller, recently sparked controversy when it sponsored Islamophobic advertisements on transit systems in major US cities including New York, Washington and Philadelphia.
Dutch far-right, anti-Islam politician Geert Wilders also gave a keynote speech at the event.
