From ABC News Headquarters in New York City, this is GMA3.

Now we want to turn to the search for Nancy Guthrie.

Investigators return to the missing 84-year-old's home 25 days after her abduction.

Trevor Alt has the latest on what they're looking for, what they're doing there.

Good afternoon, Trevor.

Hey there, Rian. And so this actually may have been the FBI's last time at the House for the foreseeable future.

Now that so much time has passed in this investigation, sources are telling us that there's a shift in strategy from the FBI as they continue to work on solving this mystery.

Three and a half weeks after Nancy Guthrie's disappearance, sources say the FBI is still

aggressively investigating the case, but many of their agents will be moving out of Tucson.

The agents return to the home Wednesday, putting up no trespassing signs and seen in that same

doorway where a mass man with a gun showed up the night of the abduction.

Sources say for the moment there is no additional investigative work the FBI needs to do at the house,

and they've moved the command post for the investigation to Phoenix, where they have more permanent resources.

But some agents will remain in Tucson, and the FBI is still working in partnership with the local sheriff's office.

Pima County Sheriff's Department.

Investigators are now pouring over the tips they've received since the Guthrie family offered a $1 million reward.

If you hear this message, if you've been waiting and you haven't been sure, let this be your sign.

To please come forward, tell what you know, and help us bring our beloved mom home.

Sources say more than 1,500 new tips came in since that reward was offered.

One of the advantages to offering a large amount of money is that somebody that might

have been hesitant to call in on this guy that was at the front door may decide that they will.

So large amounts of money can get you those critical leads.

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