Police likely will have future opportunities to catch the killer in the JonBenet Ramsey case.

That's because child sexual predators are notorious for continuing their crime rampage, and DNA databases are continually improving.

"There's no question . . . that he's going to strike again, and he's done it before," said Dr. Leigh Baker, director of the Trauma Treatment Center of Colorado. "They're serial. Very rarely does it happen once."

Pedophiles typically spend their lives seeking access to children to satisfy their sexual needs, experts say. Those who also kill are "the most serious of all violent sexual predators," Baker said.

"It is common that they do surveillance," she said. "They know their victim and do some kind of stakeout of who their victim is going to be."

That means the JonBenet killer, if he's not dead, could hit the police radar sooner or later.

The bad news is that it's been more than 11 years since the girl's death, and police have not matched the killer's DNA.

Police have found no match among more than 86,000 felons in the Colorado DNA database, which includes over 6,400 sex offenders. They also found no match in the FBI database, which includes DNA from other states.

That makes Fordham University law professor James Cohen less optimistic police will find the killer. "If he doesn't get caught re-offending, it's going to be difficult or impossible to match him to this case," Cohen said. "And the 12-year lapse of time is not encouraging."

On the other hand, it can take a decade or longer for police to catch sex offenders using DNA.

Susannah Chase, a 23-year-old CU student, was raped and bludgeoned to death in Boulder on Dec. 21, 1997. In January, a decade later, police matched DNA from semen found on her body to Diego Olmos Alcalde, a native of Chile with Denver ties who was arrested on other charges. He has been charged with murder.

JonBenet was found dead in her home Dec. 26, 1996. Police apologized to her family Wednesday, saying new DNA testing showed that relatives did not kill the girl.

They believe that an unknown man, whose DNA was found in several areas of her clothing, sexually assaulted and killed JonBenet.

Colorado police have been collecting DNA of sex offenders for more than 20 years, said Lance Clem, spokesman for the Colorado Bureau of Investigation. About three years ago, the state began adding DNA of all convicted felons, he said.

Dr. Sherryll Kraizer, a Denver-based expert on child abuse, said sexual predators typically commit 225 to 300 sex assaults on children in their lifetime.