Two American teenagers will appear in court this week charged with using a baseball bat to murder their high school Spanish teacher.
Jeremy Goodale and Willard Miller, both 16, were charged after the body of Nohema Graber, 66, was found on 3 November last year.
But new details about the case were revealed this week after a number of court documents, including search warrant information, were unsealed by a judge.
These showed that a witness supplied police with Goodale's Snapchat messages which indicated that Miller and Goodale were "involved in the planning, execution and disposal of evidence" related to Ms Graber's death.
The messages described how they had watched the teacher beforehand, how she was killed, where her body was left, where her car was parked, and how evidence was concealed and disposed of.
One of the messages said that a baseball bat was used in the killing.
Other court documents have shown Ms Graber suffered "inflicted trauma to the head".
Ms Graber's body was found under a tarpaulin, a wheelbarrow, and railroad ties at the Chautauqua Park in Fairfield, about 95 miles southeast of Des Moines in Iowa.
Police investigators have seen surveillance video showing her car left Fairfield High School and entered the park at about 4pm on 2 November.
The car was driven out of the park almost an hour later, followed by a pick-up truck.
Another witness said he had seen a male person pushing a wheelbarrow down a street in the town around midnight on 2 November.
In an interview, Miller told police he had provided a wheelbarrow from his home, according to the documents.
Many other details about the case remain sealed, including an alleged motive.
Goodale and Miller will appear in court on Thursday for a hearing on whether they should be tried as adults or juveniles.
They are currently charged as adults, as Iowa's laws say anyone 16 or over charged with a forcible felony is "subject to the same criminal procedures and penalties as adults".
The adult sentence for first-degree murder in Iowa is life in prison, although the state's supreme court banned sentences of life without parole for those under 18.
If the two are convicted in juvenile court, they could be released when they turn 18.
Goodale's trial is scheduled for August, while Miller's is set for November.
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