Derek Marsocci already had the engraved dog tags for his two new sex slaves in the cab of his truck when he went to meet a 13-year-old girl and her mother.

Instead, he was greeted by law enforcement officers in an undercover online sex sting conducted by the Baldwin City Police Department.

Marsocci, a 45-year-old interstate truck driver and a registered sex offender, was arrested Dec. 13 in the parking lot of the Great Mall of the Great Plains in Olathe. According to the Missouri Sex Offender Registry, Marsocci, who lists his home address as Centerview, Mo., has a 2002 conviction for fourth-degree sexual assault in Fort Smith, Ark.

During Marsocci’s preliminary hearing Wednesday in Douglas County District Court, Baldwin City police officer J.W. Hawkins testified that he posed online as 30-year-old single mother Tara Jones and her 13-year-old daughter, Kylie.

Hawkins said between Nov. 21 and Dec. 13, Marsocci initiated sexually inappropriate conversations in a Yahoo chat room, thinking he was corresponding with an underage girl, not a Baldwin City police officer.

“He asked if he could talk to Kylie during the first conversation,” Hawkins testified. “He said to have her sit down at the computer and talk to him and that she should be naked.”

Hawkins explained that the chats progressed to talk of “training” the two to become Marsocci’s sex slaves.

According to the chat transcripts, Marsocci wanted to impregnate the girl and keep her in the cab of his truck for a month while he traveled the country.

He even went as far as instructing Tara to pull her daughter out of school and begin home-schooling her, Hawkins said.

On Dec. 13, Marsocci arranged to meet the two in person. Instead, he met Baldwin City police officers and Johnson County sheriff’s deputies.

“He had two heart-shaped dog tags that appeared to go on dog collars,” Hawkins said, describing that both were engraved with Marsocci’s nicknames for his two “slaves.”

Marsocci’s attorney, Michael Clarke, objected to what he called a warrantless search of his client’s truck. Clarke also has filed at least seven motions, many of which question the constitutionality of the online investigation.

At the conclusion of Wednesday’s preliminary hearing, Judge Michael Malone found there was probable cause for Marsocci to stand trial on one count of enticement of a child.

A jury trial is scheduled for March 17.