Catholic school teacher David Czajkowski was accused this year of molesting students in his classroom at St. Thomas Aquinas School in Hampden. The Rev. Maurice J. Blackwell was accused in 1993 of molesting a teen-age parishioner in the rectory at St. Edward Roman Catholic Church in West Baltimore.

The circumstances were essentially the same: Both men were accused of touching children for sexual gratification. But the outcomes were vastly different. Armed with solid evidence, prosecutors secured a guilty plea of child sexual abuse May 31 from Czajkowski. However, Blackwell was never charged although investigators believed the story of his accuser, Dontee D. Stokes, who said Blackwell touched him over a three-year period, starting when Stokes was 14 or 15.

Stokes, now 26, has been indicted on charges including first-degree attempted murder. He is accused of shooting Blackwell three times last month, after confronting the priest outside Blackwell's Reservoir Hill home and demanding an apology.

The divergent endings underscore variables that affect prosecution of child sex abuse, which law enforcement experts count among the toughest crimes to handle.

Because such crimes are usually committed in secret and often are reported well after they occur, many times they lack witnesses and forensic evidence. As a result, child sex abuse cases frequently come down to credibility: the child's word against that of an adult -- and sometimes a well-respected, trusted adult such as a teacher, police officer or clergyman.

Combined, these factors are forbidding, said Susan Kreston, deputy director of the Virginia-based National Center for Prosecution of Child Abuse.

"Generally across the country, child sexual abuse is one of the most difficult types of cases to prosecute," she said.

Some children aren't supported -- or believed -- by their parents. And something else sets apart child sex abuse from other cases: Prosecutors must assess whether putting a child before a skeptical jury and the possibility of a not-guilty verdict is worth the risk of inflicting additional psychological damage.

Complicating matters further is that child victims are often too traumatized to make effective witnesses, or too terrified to face their abusers.

"I had a child in here the other day who said, 'There's no way I'm testifying. I don't care if it means that he gets to walk away. It's too scary,'" said Betsy Offermann, a clinical social worker who runs a treatment clinic for sexually abused children at Kennedy Krieger Family Center.

Part of Offermann's job is to prepare children for the likelihood that their abusers won't be punished.

"Justice is just not a big part of the reality for kids who have been sexually abused," she said.

One in three girls and one in eight boys have an unwanted sexual experience by the time they are 21, and about one in 10 children will tell an adult, according to Peggy Mainor, director of the Baltimore Child Abuse Center.

Of those cases that are reported, a small percentage make it to court. The child abuse center interviews about 1,100 children in connection with sexual abuse and assault each year. City police say they handled 768 child sexual abuse cases in 2000.

That year, the city state's attorney's office prosecuted about 245 such cases, said Althea Handy, who heads the sex offense unit. Her office was unable to furnish information about what happened in those cases.

In the Czajkowski investigation, detectives put together an ironclad case. A 9-year-old girl spoke up immediately in February after the teacher touched her back under her shirt and rubbed her chest area. Because it happened during class, other children witnessed it.

The girl -- and about 40 other fourth- and fifth-grade pupils of Czajkowski -- were quickly interviewed by a social worker or psychologist at the child abuse center, which was started in 1996 to help streamline the investigative process so that children weren't forced to tell their stories repeatedly.

The interviews, which would have taken detectives many months before the center's founding, led to at least 10 other girls who corroborated the initial victim's story. Some said Czajkowski would write problems high on the blackboard and then lift them, touching their chests as he did so. Further cementing the cases was that the girls were credible and willing to testify.

Finally, Czajkowski was repentant. He confessed to detectives that he touched the initial victim, and admitted that he had sexual fantasies about many of the girls in his class. He will be sentenced in August.

By comparison, Stokes' 1993 case seems threadbare. No one saw the alleged touching happen. Detectives conducted about a dozen interviews, but failed to drum up other alleged victims or witnesses. The child abuse center didn't exist, and so it could not help with the interviews -- a delicate process that can mean the difference between a strong case and an anemic one.

And Blackwell, a popular West Baltimore clergyman, denied Stokes' allegations. After about six weeks, prosecutors and detectives closed the investigation, which boiled down to a frustrating standoff between a priest's word against that of a teen-ager.

Depending on the individuals involved, prosecutors sometimes do pursue cases in which the sole evidence is the child's story. In such cases, the biggest hurdle for prosecutors can be the jury, Handy said, especially in "touching" cases such as that of Stokes.

"A lot of people don't take that so seriously," she said. "We take it very seriously, but unfortunately we have had difficulty getting indictments on cases like that."

Many adults have a hard time believing children, especially when they don't report abuse right away. Handy's unit unsuccessfully prosecuted a recent sexual abuse case in which a girl's sister had witnessed the alleged crime.

Prosecutors asked jurors why they acquitted the defendant.

"One of the comments was, 'Well, children lie,'" Handy said.

Nationally, over the past decade, prosecutors and police -- as they have become better educated about child sex abuse -- have brought more cases to trial, Kreston said.

The advent of DNA evidence has helped, and so has a greater understanding of how children react to abuse.

"We can now put an expert on the witness stand to explain these counterintuitive things to the jury, like why there might be a delay in reporting," Kreston said. Or why a traumatized child might talk about the abuse dispassionately.

In addition, prosecutors are asking potential jurors better questions during jury selection, such as, "Would you believe a child over an adult?" And investigators are getting better at interviewing children by not asking leading questions or using double negatives in a sentence.

Mainor, of the child abuse center, said cases like those of Czajkowski and Blackwell can be hard to prove because they challenge people's most basic beliefs: for one, that perpetrators cannot be well-liked pillars of the community yet capable of heinous crimes.

"These people don't look like monsters," she said of defendants. "They're going to be ordinary people, often whom we trust. So it goes to the core of people's feeling of safety in the world. They just don't want to believe this could happen."