After listening to an investigator who interviewed Matthew Koso and his pregnant, teenage bride in May, a Richardson County judge Wednesday said Koso, 22, can stand trial for having sex with the girl.

Richardson County Judge Curtis L. Maschman said he found probable cause to believe Koso committed first-degree sexual assault with Crystal Guyer, 14, before they married.

Maschman ordered Koso at the end of the preliminary hearing to appear in Richardson County District Court for arraignment on the charge Aug. 30. The baby is due Aug. 28.

Prosecutors have alleged Koso and the girl began having sex as early as December 2003, when she was 13 and he was 21.

Nebraska law prohibits sex between people younger than 16 and older than 18.

Meanwhile Wednesday, Nebraska Attorney General Jon Bruning, whose office filed the charge against Koso, said additional charges could be brought against Koso.

Bruning said his office has received "many credible reports" from Falls City residents stating Koso has had sex with other underage girls.

"This is an open secret in Falls City," Bruning said in an interview. "I believe these reports to be very credible."

Bruning said his office began receiving the reports "immediately" after he announced the initial charge against Koso last month.

He said his office would investigate the reports and file additional charges as "the circumstances warrant."

The possibility of additional charges angered and dismayed Peggy Koso, Matthew's mother.

"What does this man want?" she asked in an interview. "Our blood?"

She said the reports to Bruning might have come from people in Falls City who either dislike her son, or don't understand him.

She said Matthew often associated with younger people, including girls, but that he, "to our knowledge, has not been sexually active" with them.

She said Matthew once dated a 14-year-old girl when he was 19, but she described the relationship as nonsexual.

"I don't know where this (the possibility of additional charges) is coming from," she said.

Matthew Koso and Guyer are living with his mother and father, John Koso.

Guyer started her freshman year at Falls City High School Wednesday.

At the preliminary hearing Wednesday, Duane Armbruster, an investigator with the Falls City Police Department, testified he interviewed the couple separately at the department May 5, shortly after they married in Kansas.

Armbruster said Koso initially admitted he had impregnated the girl, but he said that was the only time he had sex with her. Later in the interview, Koso said he had sex with Guyer multiple times beginning in late December 2003 or early January 2004, Armbruster said Wednesday.

Koso told Armbruster the sex occurred at the home of Koso's parents, Armbruster said.

The investigator told the court Koso's statements were consistent with statements made by Guyer in the earlier interview.

Armbruster said the interviews were prompted by a report the department received from a state social services caseworker that the girl was pregnant. He said he did not know how the caseworker knew about the pregnancy.

Koso, seated next to his attorney, Willis Yoesel of Falls City, during the hearing, showed no emotion throughout the proceeding.

Just prior to the hearing, he sat on a front pew in the courtroom, dressed in black jeans, dark blue shirt, black shoes and a colorful tie with a NASCAR logo.

Immediately behind him sat his parents and older brother, Nick, who gently massaged Matthew's back.

In an interview outside the courtroom after the hearing, Assistant Attorney General Don Kleine stood by his office's decision to file the charge.

Some critics have claimed the charge will only worsen and complicate an already difficult situation for Koso and the girl.

"Our position is we will prosecute cases where adult men are having sex with children," Kleine said.

Kleine said he was troubled Koso and the girl continued to live together during the criminal proceedings against him.

Koso is out on a $5,000 bond.

"It clearly concerns us," Kleine said. "But also, a marriage has taken place. We are bound by the (U.S.) Constitution to recognize that."

Nebraska law prohibits marriage between people 16 and younger.

Koso and Guyer married in Kansas, which allows juveniles to marry with consent from their parents or guardians.

Yoesel said his client "did not pay attention" to a protection order Guyer's mother, Cecilia Guyer, got against Koso last year.

Cecilia Guyer withdrew the protection order shortly after the marriage.

Yoesel said, "A lot of protection orders are sought and issued without a real understanding of what they've created," he said without elaboration.

Reach Butch Mabin at 473-7234 or at bmabin@journalstar.com.