A convicted sex offender who has admitted abusing about 300 boys and is charged in Arlington County with molesting a teenager has fled the country, police said yesterday.

Over the objections of prosecutors, Thomas R. Koucky, 41, was released June 17 from the Arlington jail, where he was being held on a charge of sexually abusing a 17-year-old boy for several years. At the time, Koucky was on probation for similar offenses in Florida, according to court records.

"I am horrified," said the victim's mother, whose name is being withheld to protect the identity of her son. "The damage is breathtaking. . . . I had every confidence that the detectives involved in this case did everything they could to bring this guy to justice, and when he hit the justice system it broke down."

Despite a criminal record and a report detailing Koucky's predilection for young boys, an Arlington juvenile court judge on June 21 upheld his release on $3,000 bond by a magistrate.

Prosecutors were appealing that ruling in Arlington Circuit Court for a second time on Tuesday when Koucky did not appear in court. His bond was revoked, but police learned late Wednesday that he had already skipped town, catching a flight the previous week from Atlanta to Guatemala.

Yesterday, Arlington police said they are working closely with U.S. Customs and Border Protection and the U.S. Marshals Service to apprehend him.

"There was ample reason this guy should have been held and that wasn't done, and now he's gone," Arlington County police spokesman Matt Martin said. "We're dismayed."

At a hearing before juvenile court Judge George D. Varoutsos, investigators said Koucky admitted in an April 27 report to being attracted to boys ages 14 to 17, experiencing trouble controlling his fantasies and committing numerous sex acts on minors including, by his own report, "abusing around 300 boys."

"I am strongly attracted to males," he is quoted as saying in the report. "If I walk out this door and a young boy is standing there and I'm around, it's all over."

Although Koucky was registered as a sex offender in Virginia, his sex crimes were not considered violent, so his name appeared on a list available only to qualifying groups such as day-care centers, schools and nursing homes.

Koucky's attorney in the Arlington case did not return multiple phone calls late yesterday.

As far back as August 1990, Koucky was arrested by the Collier County Sheriff's Office in Florida and charged with lewd and lascivious behavior and solicitation for prostitution, for allegedly approaching a 13-year-old boy at a neighborhood pool and asking him sexually suggestive questions before offering him money in exchange for sex, according to court papers filed in Charles County District Court in La Plata.

The lewd and lascivious charge was dismissed, and Koucky pleaded guilty to soliciting for prostitution and was placed on 10 years' probation.

He was arrested again in December 1993 by police in Frederick on charges of soliciting a 16-year-old boy for prostitution. Police said that the boy was a convenience store clerk when Koucky offered him $500 in exchange for sex.

According to the court papers, it was the Frederick case that required Koucky to register as a sex offender in the District, where he lived before moving to Arlington in October 2002, although there is no record of any criminal wrongdoing in Washington.

While he lived in Arlington, Koucky worked in Waldorf as a real estate agent in the Berry Valley subdivision, where he sold townhouses.

In November 2002, the Charles County Sheriff's Office was told that Koucky had asked at least five boys ages 10 to 14 in the subdivision about sex acts. Investigators said Koucky agreed to watch over a client's 10-year-old son after school in a model unit because the townhouse she purchased was not ready at the time.

The boy told police that in September 2001, when Koucky was baby-sitting for him after school, Koucky asked the boy several sexually suggestive questions. Four other boys who frequently went to the subdivision told police that Koucky made similar sexual comments to them and showed them pictures of naked men and women.

In the summer of 2001, in an upstairs room at the Berry Valley model unit, Koucky allegedly touched one of the boy's buttocks before talking to the boy about sex acts, according to court papers. On Jan. 15, 2003, Koucky was charged with child abuse and fourth-degree sex offense in connection with the Berry Valley allegations. The charges were later not pursued, though court records do not specify why.

Koucky was also charged with failing to notify Maryland officials that he was on Florida's sex offender registry. He was required to register in Maryland because he worked there. He was sentenced to six months in prison, but was released after serving four months, according to court records.

After his release on Aug. 23, 2003, Koucky lived in Arlington on the 1000 block of South Edison Street. In October 2003, Koucky's parole officer told Maryland authorities in a letter that Koucky "has requested permission to travel outside of this country." The parole officer denied the request.

The mother of the Arlington victim said her son was hospitalized after threatening to kill himself as a result of the alleged abuse. She said Koucky was a flight risk and should not have been allowed to post bond.

" 'Oh, no,' they kept saying, 'He's got property, he's got a job, he's got connections, he's not a flight risk,' " the mother said. "Well, I was right."

Staff writers Elaine Rivera, Henri E. Cauvin and Avis Thomas-Lester contributed to this report.

Thomas R. Koucky flew to Guatemala, police said.