The pinger locator detected, then lost, two transmissions on Saturday and Sunday.
Houston said that officials could not confirm that the pulses came from Flight 370 until they visually identified wreckage.
"I believe we are searching in the right area," he added. "What we're picking up is a great lead."
ALERT: Australian officials say they've detected total of 4 signals in search area for #MH370, need to find wreckage before confirming— UPI.com (@UPI) April 9, 2014
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