22-year-old Matthew Koso could face a criminal trial. He's charged with first degree sexual assault of an underage girl who is now his wife. The girl was just 13-years-old when they found out she was pregnant with Koso's child. After that, the two made arrangements to get married in Kansas. Wednesday was Koso's preliminary hearing. Inside the courtroom, the prosecution called Fall City Assistant Chief Armbruster of the Falls City Police department to testify about an interview he had with Matthew Koso on May 4th.

Armbruster said, "Koso told me that they had a sexual relationship and she was pregnant by him." Koso also told Armbruster that, "they were still seeing each other and got married the day before" on May 3, 2005.

The judge determined that testimony was sufficient evidence to set an arraignment. Donald Kleine, state prosecutor, says the Attorney General's office is taking this case very seriously.

"The Attorney General's office will vigorously prosecute adult men that are having sex with children and that's what this case is about," says Kleine.

But Koso's defense attorney, William Yoesel, argues that there are other circumstances to consider.

"I hate to talk about Matt that much, but he's got some limitations. He's 22 years of age, but he doesn't function as a 22-year-old. He's an adult and he doesn't necessarily function as an adult," says Yoesel.

Koso's wife was not present at the hearing her due date is August 28.