Miller was arrested at his home in Grabill on Sunday, July 15 for the murder of 8-year-old April Tinsley in 1988.
And in the intervening years, the killer - whose DNA was found on April's underwear - taunted cops and citizens with lurid notes.
Two years after the murder, police found a note on a barn close to where her body was found in DeKalb County.
Prosecutors have until Thursday to file formal charges.
John Miller, left, has been accused of the 1988 rape and murder of eight-year-old April Tinsley, right.
April's family left Fort Wayne in 1991 but returned five years ago.
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"Hi honey. I been watching you", one note released by the Federal Bureau of Investigation read.
IN police say cutting-edge genealogy and DNA techniques helped solve an infamous, 30-year-old cold case.
One read: "I kill 8 year old April Marie Tisley I will kill agin".
According to a probable cause affidavit, a FWPD detective arranged for DNA testing to be done on the April Tinsley suspect evidence sample in May 2018.
Miller said he dumped her body April 2 and later drove by the site, according to a probable cause affidavit.
Police used DNA taken from condoms recovered July 6 from outside Miller's home and in 2004 from three other locations to identify the alleged killer. Her body was discovered three days later northeast in a ditch along Country Road 68 in Spencerville. "D$3 id you find the other shoe haha I will kill again". Along with the condoms, police found notes saying the person who left the condoms had raped and killed Tinsley.
The Fort Wayne Police Department submitted the suspect's DNA to Parabon NanoLabs, and this month the firm's genealogist CeCe Moore was able use public genealogy databases to narrow down the suspects to two brothers in the Fort Wayne area.
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Investigators developed a DNA profile from the condoms, and "it was determined to be consistent with the profile developed from the underwear of April M. Tinsley".
Miller wore a blue jumpsuit, his feet and hands shackled as he appeared Monday before an Allen County judge, who asked him if he understood the preliminary charges he faces.
Court documents said that when police arrived at Miller's home Sunday, they asked him if he knew why they were there.
In 2004, Tinsley's murderer left four such disturbing notes at some residences in the Fort Wayne area.
Last April, to mark the 30th anniversary of April's murder, Janet Tinsley made a decision to hold a balloon release in a small neighborhood park dedicated to April near her home.
Police released few details about Miller, but said that it appeared he lived by himself.
According to the Indy Star report, Miller confessed to kidnapping, raping and murdering April in his trailer on April 1, 1988, before dumping her body in a ditch.
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