Article continues below advertisementThe search for Nancy Guthrie is intensifying - and investigators are now zeroing in on two key dates leading up to her disappearance.The FBI is asking neighbors in Tucson to review and submit any CCTV footage captured between January 11 and January 24. Authorities believe those two days could be critical, as experts suggest someone may have been secretly watching the 84-year-old's home in the weeks before she vanished.Article continues below advertisementSource: @BrianEntinInvestigates/YouTubeNancy Guthrie went missing in Arizona.