Richard Allen pleaded not guilty to the murders of best friends Abby Williams, 13, and Libby German, 14. Their bodies were left in the woods on Feb. 13, 2017, and discovered the next day.
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The crime gained national attention when police released an image of the suspect and a clip of his voice -- a recording of him saying "down the hill" -- which was recovered from Libby's phone.
Allen admitted to being on the trail the day of the murders but denied involvement.
Here's a look at the trial's major takeaways:
How the girls died
For more than seven years, investigators stayed tight-lipped about how the girls were killed, not revealing if their deaths were caused by a knife, a gun or some other weapon, and not disclosing if they were sexually assaulted.
Then, prosecutor Nick McLeland revealed in his opening statement that the girls' throats were cut.
Pathologist Dr. Roland Kohr, who performed the autopsies, testified that Abby had a 1-inch-deep, 3-inch-long incision wound on her neck.
Libby had several incision wounds on the right side of her neck, Kohr said, the largest being about 3.5 inches long.
Kohr said he initially thought a serrated knife was used to cut the girls' necks, but he began to believe during final trial preparations that a box cutter may have been used.
Libby's body was found naked, prosecutors said, but rape kits concluded there was no DNA evidence showing the girls were sexually assaulted, according to testimony from a forensic scientist.
Witnesses recollect 'bridge guy'
After Abby and Libby crossed the Monon High Bridge, they saw a man behind them, and Libby started a recording on her phone, McLeland said. The man pulled out a gun and ordered the girls to go "down the hill," McLeland said. The girls complied, McLeland said, and then the video on Libby's phone stopped recording.
That video clip from Libby's phone of the "bridge guy" was released early in the case as investigators asked the public to help identify him.
During Allen's trial, a pair of teenage girls who were on the trail that day shared their recollections of the "bridge guy" with the jury.
Railly Voorhies said the man she saw was overdressed for the weather, had on dark clothes, was wearing a hat and had his hands in his pockets.
The prosecution pulled up a photo of the "bridge guy" and Voorhies said, "That was the man I had waved at on the trail."
Breann Wilber, who was on the trail with Voorhies, testified she also noticed the man who was overdressed for the warm weather.
She said the man was walking with a "purpose," didn't respond when Voorhies said hello and gave off "weird vibes."
Wilber said that, when she saw the picture of the "bridge guy," the "first thing I thought is -- that is the person I saw on the trail."
During cross-examination, the girls were pressed on how their description of the man changed over time.
Timeline of the crime
A timeline of the crime was revealed through data from Libby's phone, which was recovered from under Abby's body.
Libby's phone showed the girls were dropped off at the trail at about 1:40 p.m. and were near the Monon High Bridge at 2:05 p.m., Indiana State Police Sgt. Christopher Cecil testified.
At 2:14 p.m., Cecil said Libby took the infamous "bridge guy" video.
Phone records noted a change in longitude, altitude and elevation at 2:31 p.m., Cecil said, meaning Libby's phone was moving. By 2:32 p.m., Cecil said the teen's phone stopped and never moved again.
Cecil testified that Libby's phone gradually powered down throughout the night, died at 10:32 p.m. and then woke with a spike at 4:33 a.m. Cecil said that is when her phone received 15 to 20 text messages all at once. One of the messages, sent nearly 12 hours earlier from Libby's grandmother, said, "You need to call me now!!!"
Cecil said he did not know the reason for that gap in time.
Twenty-three devices were seized from Allen's home but none of them tied Allen to the girls or the crime scene, Cecil said.
Allen's mental state, confessions in jail
Allen's mental state at the time of his multiple confessions while in custody became a major focus of the trial.
Allen was arrested in the fall of 2022. By spring 2023, his behavior took a turn. Allen's strange behavior in custody included hitting his head on the wall, washing his face in the toilet, refusing food, eating paper, smearing feces in his cell and putting feces on his face for two hours, according to testimony from corrections officers.
In the spring of 2023, Allen also began confessing to the murders multiple times to his wife, to a psychologist and to corrections officers, according to testimony.
Psychologist Monica Wala testified that, in one of Allen's confessions to her, Allen told her he saw the girls on the trail and followed them to the bridge.
Allen said he ordered the girls "down the hill" and intended to rape them, but then he saw something -- either a person or a van -- and was startled, Wala said. Allen told her he ordered the girls across the creek, slit their throats and covered their bodies with branches, according to Wala.
Allen also allegedly confessed in multiple jail phone calls to his wife.
Allen told his wife, Kathy, "I did it. I killed Abby and Libby."
"No, you didn't," she said. Allen replied, "Yes, I did."
"Why would you say that?" Kathy said. "I know you didn't. There's something wrong."
Allen spent 13 months in solitary confinement, and a neuropsychologist who testified for the defense said that can change an inmate's brain chemistry.
The neuropsychologist said Allen experienced hallucinations, psychosis and suicidal ideation.
One corrections officer, Michael Clemons, testified for the prosecution that Allen told him, "I, Richard Matthew Allen, killed Abby and Libby by myself. No one helped me." Clemons said Allen would shout to other inmates, "I'm not crazy, I'm only acting like I'm crazy."
Another corrections officer, Michael Roberts, testified that on April 23, 2023, Allen said, "I killed Abby & Libby. My wife wasn't involved. I want to confess."
Days later, according to Roberts, Allen said, "Can I talk? Can you listen I killed Abby & Libby? How do I prove I'm insane?"
Dr. John Martin, who treats inmates, was called as a state rebuttal witness.
Martin said he met Allen in November 2022 shortly after he was arrested. Martin said Allen arrived at the jail with a Prozac prescription because of a history of depression, but Martin said he considered him stable.
It wasn't until April 2023 when Allen started showing signs of psychosis, according to the doctor.
Martin said he got a call on April 13 to come visit Allen. Martin said he found Allen naked on a mattress, covered in feces, and he was told he had been eating it.
Martin said he put Allen on an anti-psychotic drug; he said it took until April 25 to get the medication figured out and for Allen to show signs of improvement.
By May 18, 2023, Allen was showing no signs of psychosis, according to Martin.
On June 20, 2023, Allen -- while still showing no signs of psychosis -- told Martin that he "wanted to apologize to the families and his victims," Martin testified.
Martin said Allen hadn't shown any symptoms of psychosis for several weeks and was under no pressure to say anything.
The gun
The prosecution's key evidence is police analysis of Allen's gun, which determined that the .40-caliber unspent round discovered by the girls' bodies was cycled through Allen's Sig Sauer Model P226.
But a defense witness, Dr. Erin Warren, called that into question.
The defense asked Warren to review the work of Melissa Oberg, the former Indiana State Police crime lab technician who examined the unspent round found at the scene and compared it to Allen's gun.
Warren called it an "apples to oranges" comparison, saying Oberg compared the initial round -- which had been cycled, not fired -- to a bullet fired from Allen's gun.
Oberg said on the stand earlier that an "ejector mark was an ejector mark," regardless of whether a round was cycled or fired.
Warren disputed that testimony, saying the lab needed to identify tool marks under the same conditions in which the bullet was found.
Jurors had 15 questions for Warren about the testing method on the cartridge, which was notably more questions than most witnesses received from the jury.
Closing arguments
In closing arguments, defense attorney Brad Rozzi argued his client's innocence, noting how Allen stayed living in Delphi in the years following the crime, even though he had the chance to leave at any point.
Rozzi reminded the jury that Allen came forward on his own in 2017 to tell police he was on the trail the day of the murders. Rozzi said Allen cooperated in his first interrogation in October 2022 and went back for questioning a second time, even though he knew he was likely a suspect at that point.
Rozzi highlighted that hours of video interviews from 2017 were lost.
He also brought up the 13 months Allen spent in solitary confinement, saying all the state wanted to spotlight was what Allen said, not his condition.
Rozzi argued the Indiana State Police lab couldn't exclude that the gun belonging to local resident Brad Weber was the one that cycled the round found by the girls' bodies, and he said Weber changed his story about going straight home on the day of the murders.
In the prosecution's closing, McLeland said the state had proven Allen is the "bridge guy," and he reminded jurors the 2016 black Ford Focus spotted near the trail that day was the only one registered in the county -- and it was Allen's.
Despite doubts from the defense, McLeland said the state proved the unspent round found between the girls' bodies cycled through Allen's gun, and he said testing was confirmed three times by the technician's boss.
McLeland also drilled down on Allen's numerous confessions, playing for the jury the phone call confessions Allen made to his wife. McLeland said Allen's confessions were "unprovoked, unpressured [and] of his own free will," and he said Allen was not showing any signs of psychosis at the time of many of his statements.
The prosecutor highlighted the fact that Allen mentioned seeing a van at the scene in one of his alleged confessions. McLeland reminded jurors that Weber was believed to be driving his van home from work around the time of the murders. McLeland said that was "something only the killer would know."