He made two appearances on CNN's Nancy Grace Show. On August 25, he said he took and passed a polygraph test concerning Katelyn's disappearance. When Carter appeared on the show again Wednesday, he said he had NOT taken a polygraph. But he would take one if asked.
Police are not discussing details of the investigation. Carter has not returned phone calls for a comment.
Police have also determined where the cell tower is located that received the last signal from Markham's phone. Police are not revealing the location of that cell tower.
Over 100 volunteers fanned out across the area Thursday looking for Katelyn. The next big search is scheduled for Saturday.
Volunteers are asked to check in at the Texas EquuSearch's local headquarters at Fairfield West Baptist Church, 5345 Muskopf Road. Long pants and good walking shoes are recommended.
With the required resources and volunteers, he said all that's needed to find Katelyn Markham "is a little bit of luck."
For Katelyn's father Dave Markham, some days are better than others, but he said he's happy with the efforts of the police department, and especially thankful for the community's response.
"The community is concerned. The community is just rallying behind it. It's comforting, soothing."
Markham was reported missing Aug. 14 by Carter and her father. Police say there are no signs of foul play, but no reasonable explanation as to what could have led to her disappearance.
A $25,000 reward is being offered for information leading to Markham. Call Fairfield police at (513) 829-8201 or CrimeStoppers at (513) 352-3040.