welcome back. in the search for missing malaysia flight 370, investigators say they have their most promising lead yet. >> absolutely. a u.s. pinger locator aboard the australian ship ocean shield has now detected more signals consistent with those emitted by aircraft flight recorders. officials say the search will now go under water to locate possible wreckage, a key piece of this ongoing investigation now, which has lasted more than a month. brian todd joins us from washington to discuss these new developments, because, brian, what becomes key now are these this pinger locator. and essentially, the search now goes underwater. >> that's right, errol and rosemary. what we've been doing over the past couple of weeks, my team and i have been reporting on the capabilities of the towed pinger locator, the device which detected these signals overnight. and also, the other device on the ocean shield along with the