When investigators interviewed Cristhian Bahena Rivera, they showed him a photograph of a black Chevy Malibu that drove back and forth in the area where Mollie Tibbetts was running on the evening she vanished, authorities said.

"Yes, that's my car," Bahena Rivera said, court records show.

The minor new detail in the state's theory about the death of Tibbetts, whose disappearance and killing were followed across the country, was revealed Wednesday in a court filing by prosecutors.

Bahena Rivera's defense team in September filed a motion arguing prosecutors must tell them what specific actions he was accused of taking to kill the 20-year-old University of Iowa student. His lawyers said details included in documents charging him with first-degree murder do not offer enough information for them to mount a defense in the case. (Those documents are not public.)

In response, prosecutors said in a public filing that the motion for a bill of particulars cannot be used to obtain the state's evidence. Bahena Rivera's attorneys filed the motion before receiving any discovery, which prosecutors said will further support the charge.

"The filing of this motion is premature," Scott Brown and Laura Roan, the Iowa assistant attorneys general prosecuting the case, said in court records.

More:Mollie Tibbetts: Complete coverage of Iowa woman's disappearance, death

A report from the Iowa Division of Criminal Investigation will be finalized and delivered to Bahena Rivera's attorneys Friday. Further forensic testing was expected to be done in November, prosecutors said.

Authorities said Bahena Rivera, 24, killed Tibbetts on July 18. Five weeks later, as the search for Tibbetts gained national attention, he used his phone's maps to determine the route he traveled and later led police to her body in rural Poweshiek County by memory, officials said.

Police said Bahena Rivera told them he pursued Tibbetts in his car while she was jogging that night before parking, getting out of the car and running behind and alongside her. When Tibbetts told Bahena Rivera she was going to call the police, he "panicked and got mad," according to a criminal complaint.

"He then 'blocked' his 'memory' which is what he does when he gets very upset," authorities wrote in charging documents. "And doesn't remember anything after that until he came to at an intersection."

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Bahena Rivera has pleaded not guilty to the charge. His lawyers, Chad and Jennifer Frese, argued in the motion that the charging documents failed to provide any information about how prosecutors believe he killed Tibbetts.

His attorneys also argued prosecutors have not provided information about how they intend to show the killing was premeditated. A crime scene report and two lab reports have not been provided to them, they said in the motion.

But in their resistance, prosecutors said an autopsy found Tibbetts died of multiple sharp force injuries, a cause of death that established a premeditated and deliberate killing.

Prosecutors were not obligated to prove where Tibbetts died. Like in any criminal case, the time she died can be proved with circumstantial evidence, the state's attorneys said.

Bahena Rivera's trial has been set for April 16, 2019. If convicted, he would be sentenced to life in prison without the possibility of parole.

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