According to what I've read he didn't confess until after he was arrested. he was arrested witht eh cooperation of law enforcement agencies here and in Thailand. Also, at least Patsy knew about the upcoming arrest:

Text of a statement from John Ramsey, the father of JonBenet Ramsey, released Wednesday, Aug. 16, 2006:

      "I want to have only very limited comment on today's arrest because I feel it is extremely important to not only let the justice system operate to its conclusion in an orderly manner, but also to avoid feeding the type of media speculation that my wife and I were subjected to for so many years.

      "I do want to say, however, that the investigation of the individual arrested today in connection with JonBenet's death was discussed with Patsy and me by the Boulder district attorney's office prior to Patsy's death in June.

      "So Patsy was aware that authorities were close to making an arrest in the case and had she lived to see this day, would no doubt have been as pleased as I am with today's development almost 10 years after our daughter's murder. Words cannot adequately express my gratitude for the efforts of Boulder District Attorney Mary Lacy and the members of her investigative team."