"We have to find her first. Once we've found her, then we'll know," Centeno said.
About 30 FBI agents joined state police in their search for Capino in late September, state police said. Information about the girl's disappearance and the FBI's involvement in the case were made public Wednesday.
The FBI agents helped state police go door-to-door through the girl's West Ridge Hills neighborhood and collected "possible evidence from several locations," state police said.
Centeno and other state police officials would not comment on the nature of that possible evidence, or the locations from which it had been collected.
Centeno said the FBI has assisted closely in the case. He said the FBI can devote more resources to such a case, and the agency has national jurisdiction.
"The FBI has a great policy of helping children be located," Centeno said.
The girl has a history of medical problems and needs medication, Centeno said. He would not describe her health problems, citing the confidentiality of medical records.
He said the condition was not life-threatening, but a lack of medicine could cause problems for her.
The girl's parents told investigators their daughter left the house on Aug. 17 after an altercation with them, Centeno said.
Since then, no one has reported seeing her, and neighbors and her friends have been questioned, but without results, he said.
The girl is described as white, about 5 feet 2 inches tall, with short, blond hair and blue eyes. She weighs about 110 pounds.
When last seen, she was wearing a pink and orange swimsuit top, green denim shorts and black slip-on shoes, Centeno said.