CBS News National Correspondent Hattie Kauffman reported on "The Early Show" Monday and has the latest details in the case.
As authorities continue an exhaustive search around Portland, they are also looking for clues close to home, asking whether anyone saw Kyron's stepmother Terri Horman at Skyline Elementary the day he vanished.
Multnomah County Sheriff Capt. Jason Gates told reporters Terri Horman is the last known person to have seen Kyron before he disappeared.
Terri says she snapped a picture of Kyron on June 4 at the school science fair, and left him before his first class. New fliers ask parents and students whether they spotted her Ford F250 truck that day.
Laurie Levenson, a former federal prosecutor, told CBS News, "We don't really have any hard evidence yet that she is responsible for the boy going missing, but all of the investigation seems to be keying in on her."
Investigators have reportedly reviewed Terri Horman's cell phone records and given her a second polygraph exam.
Levenson said, "This investigation has gone beyond a missing boy investigation to a real criminal investigation. It seems to suggest that they know nothing good has happened to this young man and they're keying in on who they believe is responsible."
But at this point, Kauffman said, police are not naming Kyron's stepmother a suspect.