Miller, of Grabill, Ind.is alleged to have abducted, raped and murdered the little girl in April 1988 as she walked home from a friend's house in Fort Wayne.
Miller has been charged with murder, child molestation and confinement.
He is scheduled to appear in court on Monday.
"I kill 8 year old April M Tinsley", the barn read, according to a recently filed police affidavit.
Miller told detectives that the next morning he dumped her body in a ditch and that he drove by the next day when he did not see it on the news according to the affidavit.
On May 21, 1990, police were called to a barn at Schwartz Road and IN 37, where writing had been seen on the barn that appeared to show the suspected killer taking credit for killing Tinsley.
In 2004, 16 years after April's death, the killer left threatening notes, photos and used condoms on three girl's bicycles and in a mailbox in the Fort Wayne area.
The testing was able to narrow down the suspects in the case to Miller and his brother on July 2, the affidavit says. "I been watching you I am the same person that kinapped an rape an kill Aproil Tinsely you are my next vitem". "(D) id you find the other shoe haha I will kill again".
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". Parabon Nanolabs is a genetics company that has been credited for helping to solve several cold cases recently, including the arrest of Joseph James DeAngelo, the man known as the "Golden State Killer".
The investigation of the case also is continuing by the Fort Wayne Police Department and the Indiana State Police, with assistance from the Federal Bureau of Investigation, Allen County Sheriff's Department and the prosecutor's offices in Allen and DeKalb counties, the prosecutor's office announcement said.
He said he choked her, and that it took ten minutes for April to die. That is when a detective arranged for DNA testing and analysis to be done on the suspect's evidence sample at Parabon NanoLabs. Investigators then examined Miller's trash and found three used condoms that matched the DNA evidence from the suspected killer. This time, police found three used condoms in three different in towns with notes attached to them.
He told police he abducted the girl, sexually assaulted her and then killed her to keep her from reporting him to the police, according to court documents. Authorities plan to offer additional information at a news conference on Tuesday.
DNA from Miller's garbage matched DNA from the crime scene and from the taunts, and when police brought him in for questioning, he confessed to the disturbing killing, the affidavit states. He also had found one of her shoes in his auto, and he threw that out the vehicle window along the ditch as he drove by.
Last April, to mark the 30th anniversary of Aprils murder, Janet Tinsley made a decision to hold a balloon release in a small neighborhood park dedicated to April near her home.