WHO-TV reported that Corey climbed over a fence to access the site of the tower. It was not clear how high he managed to climb before falling to his death.
The preliminary findings of the autopsy indicated that the eighth-grader's injuries were not survivable, the Times-Republican reported. He likely died the night he left home on Jan. 22.
Toxicology results on the teen are pending, Tupper said.
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Corey's parents reported him missing the morning of Jan. 23 when they found his bedroom empty, the Times-Republican reported. Security footage from the home showed him leaving around 11 p.m. the night before, during a winter weather advisory.
The teen was upset following an argument with his parents, during which they took his cellphone away.
"Anyone with kids has had discussions with their children about household rules," Tupper told NBC News. "This was a typical parent-teenager interaction. No anger. Nothing extraordinary."
More than a dozen law enforcement agencies from around Iowa joined Marshalltown first responders in four days of search efforts, which were hindered by harsh winter conditions. More than 6 inches of snow fell the night Corey left home and the following day.
Temperatures topped out at 29 degrees while the boy was missing and the lowest temperature, recorded Friday morning, was -9 degrees, NBC News reported.
Corey's body was discovered shortly before noon Sunday in an area of Marshalltown described as secluded. Google Street View images from June 2018 show multiple communications towers in the block where he was found.
The funeral home handling the boy’s arrangements is across the street from the area where his body was found.
"We ask that everyone is cautious in how they talk about this and try to stick to the facts," Tupper told the Times-Republican. "I realize that people are going to have questions, but the family has been through a lot.
“We want to just continue to pray for Corey and the Brown family.”
Corey's obituary states that a funeral Mass will be held at 10:30 a.m. Saturday at St. Henry Catholic Church in Marshalltown. A visitation will be held from 4 p.m. to 7 p.m. Friday at the church, with a candlelight vigil immediately following the visitation.
The teen will be buried at Riverside Cemetery.