"I tend to be structurally agnostic, but many of the clients we work with tend to prefer" ETFs, says Mr. Fulton of PowerShares.

WSJ: ETNs Take Off but Have Far to Go

"They've killed my son, and now they're trying to kill his reputation, " said Sybrina Fulton, Mr. Martin's mother.

WSJ: Florida Teen's Killing Sparks New Allegations

Mr Brown had left to catch a flight to California by the time officers arrived at his home, Fulton County Police spokesman Kurtis Young said.

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