BOULDER, Colorado (CNN) -- JonBenet Ramsey slaying suspect John Mark Karr was on his way to Colorado on Thursday afternoon.
Karr was handcuffed and placed aboard a waiting Beech King Air twin tubroprop airplane registered to the state of Colorado.
Karr was driven by sheriff's deputies onto the tarmac at the airport in Long Beach, California, and the plane took off at about 4:05 p.m. ET. According to the flight plan, Karr will arrive at the municipal airport in Boulder at about 6:45 p.m.
In another development, prosecutors revealed in court papers that investigators learned Karr's identity just five days before he was arrested in Bangkok, Thailand.
The evidence against Karr was "only developed recently," prosecutors said, arguing to keep an affidavit detailing that evidence under seal.
The investigation "is in its very early stages," prosecutors said. Among the work that remains to be done, the motion said, are many witness interviews.
Karr, a 41-year-old schoolteacher, is being held on suspicion of murder, kidnapping and sexual assault of a child in connection with the slaying of the 6-year-old beauty pageant competitor.
"It is crucial that people we interview provide information that is as accurate as possible, unaffected by influences other than their own resources and their best recollections," prosecutor William F. Nagel wrote.
Meanwhile, police in Sonoma County, California, said Karr came to their attention in 2001.
Investigators looking into the slaying of a 12-year-old girl learned Karr had a "fascination" with the murders of JonBenet and Polly Klaas, the Sonoma County sheriff said.
Child porn investigation
Lt. Dave Edmonds, a sheriff's spokesman, said the department launched an investigation that ultimately resulted in child pornography charges.
But, he added, there was no indication that Karr knew details about JonBenet's death that had not been publicly released.
"In a few instances, while he (Karr) seemed to be wondering about the JonBenet Ramsey murder, he made uncertain allusions to placing himself in the killer's role," Edmonds said.
"However, we never uncovered any confession statements, overt murder evidence or other indications that John Karr possessed secret knowledge that only the murderer of JonBenet Ramsey would know."
Polly Klaas, 12, was kidnapped from a slumber party at her home in Petaluma, California, and killed in 1993. Richard Allen Davis confessed to her murder and is on California's death row.
Karr never stood trial on the five Sonoma County child pornography counts because he skipped bail. The arrest warrant for those charges will be served "after Karr's matters in Colorado are resolved," said sheriff's spokesman Edmonds.
Chatty suspect
Karr has made statements to reporters -- and allegedly to authorities -- about JonBenet's death. He continued even after he reached the United States from Thailand, a source involved in his transfer said.
As he was being driven to the Los Angeles County jail, Karr began talking calmly to himself while looking out the window, the source said.
"Everybody says I couldn't know my way around the house, but I got in the house around 5 o'clock ... and I stayed there all night," the source quoted Karr as saying. (Watch how Karr keeps on talking -- 2:23)
Karr also said that "they" -- meaning the Ramseys -- did not come home until about 10 p.m. He also repeated what he earlier told reporters -- that JonBenet's death was an accident, and that he was with her when she died.
Karr also told a Thai officer that he had "sex" with JonBenet before her December 26, 1996, death but "there was no penetration," a Thai official said Wednesday.
"Karr then said, 'There are so many ways to have sex,' then he went quiet," Thai Immigration chief Gen. Suwat Tumrongsiskul said.
JonBenet's beaten and strangled body was found in the basement of the family home in Boulder, Colorado, the day after Christmas.
Karr's troubles began at an early age, according to longtime family friend George McCrary. Karr's mother was an evangelist and became delusional, believing demons were in her children -- especially John, he said.
The woman needed psychiatric treatment after she attempted to kill Karr, not yet 2, with fire, McCrary said. Neither Karr's family nor their attorney has been available to verify his account, however.