Video: Investigation Into Poisoned Letters Asks If Elvis Impersonator Was Framed

Did someone try to frame Elvis impersonator Paul Kevin Curtis by sending ricin-tainted letters to President Barack Obama and other officials?That's the question investigators are trying to answer now that federal prosecutors have dropped charges against Curtis, a law enforcement source told CNN on the condition of anonymity.

Reports in numerous media outlets have indicated a second home has been searched in connection with the investigation, and CNN reporters have visited a Tupelo, Mississippi, house where FBI investigators wearing hazardous materials suits have conducted a search.

However, CNN is not identifying the homeowner because federal authorities have not linked the owner to the ricin investigation.

Prosecutors initially charged Curtis April 17 with sending a threat to the president after letters containing a suspicious powder triggered security scares around Washington. Authorities dropped the charges Tuesday after new information became available, U.S. Attorney Felicia Adams said.

Curtis' attorney, Christi McCoy, said her client has been framed by someone who used several phrases Curtis likes to use on social media.

The letters read, in part: "To see a wrong and not expose it, is to become a silent partner to its continuance."

They were signed "I am KC and I approve this message," a source told CNN.

Each letter had a Memphis, Tennessee, postmark and no return address.

Curtis called his arrest surreal.

"It's like a train has been lifted off my shoulders," Curtis told CNN's "Piers Morgan Live" on Tuesday. "I'm overwhelmed. I'm extremely happy to be vindicated and out and able to see my kids."

The letters -- sent to Obama; Sen. Roger Wicker, R-Mississippi; and Sadie Holland, a Justice Court judge in Lee County, Mississippi -- touched off anxieties in Washington and elsewhere in the wake of the bombing of the Boston Marathon. The two incidents were unconnected, officials said.

The FBI said the letters tested positive for ricin, a toxin derived from castor beans that has no known antidote. No illnesses have been reported.