They said he beat the girl in the head with a motorcycle helmet, stomped on her throat “to silence her” and stripped her nearly naked, according to the Detroit Free Press.

They said he killed her and left her body along the Macomb Orchard Trail.

In court, prosecutors pointed to crime-scene photos, saying the killing lasted about 10 minutes — during which Millsap shed tears and grabbed at leaves on the ground. Then, prosecutors used data from a fitness app on her cellphone and images from Google Earth to track her killer’s movements.

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“To me, that’s the smoking gun,” Armada Police Chief Howard Smith said, according to MLive.com. “That’s what kind of cinched it for me.”

VanCallis, a 34-year-old from Goodells, Mich., was charged with murder, kidnapping and assault. Following a two-week trial, he was convicted by a jury Monday in a Macomb County court and will be sentenced in March.

Under Michigan law, according to the Detroit News, he faces life in prison.

Macomb County Assistant Prosecutor William Cataldo told jurors that in VanCallis’s case, “an absence of evidence isn’t evidence of absence,” according to MLive.

“Yes, there is no physical evidence, but it certainly wasn’t for lack of trying,” he said. “We can’t get to what he’s already thrown out before we know it’s him.”

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In the end, a source familiar with the case told the Detroit News, jurors felt there was “overwhelming” evidence to convict VanCallis for beating the girl to death.

Cellular evidence has become a controversial topic in trials.

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Perhaps the best-known controversy surrounds Adnan Syed, who was convicted of murdering his former high school girlfriend in 1999, largely on the basis of cellphone data. His case gained national attention though the podcast “Serial” and has since made its way back to the courtroom.

For years, investigators have used cellphone records to determine where and when perpetrators picked up a phone — an attempt to show whether they were near crime scenes. But experts have argued that using cellphone towers to trace someone’s whereabouts is risky since signals do not always tap the nearest tower. In addition, they say, tower ranges vary and overlap.

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“It’s not really junk science — it’s misinterpreted science,” Larry Daniel, a forensic expert from Raleigh, N.C., told The Washington Post in 2014. “It is useful and can be used. But in the hands of a novice, this is dangerous science.”

In the Michigan case, police believe, based on phone records, that VanCallis had traveled to Armada, a small town in the eastern part of the state, to visit his brother, according to MLive.

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Witnesses told police they had seen a man matching his description riding a motorcycle near the trail. Police said he was also seen on surveillance footage from a nearby gas station, according to the news site.

Smith, the town’s police chief, said he believes April Millsap denied VanCallis’s advances and that he left, according to MLive.

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She then texted her boyfriend, police said, writing, “I think I almost got kidnapped.”

VanCallis grew angry, Smith said, and returned to kill the girl.

Millsap died from blunt-force trauma to the head and asphyxiation.

A passerby discovered her battered body along the trail about 8:30 p.m. July 24, 2014, soon after she set out for her walk, according to MLive. Her shirt had been partly removed, her bra ripped and pants pulled down, according to the Detroit Free Press.

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An autopsy showed she had a bruise above her eye — one the prosecutor argued matched VanCallis’s motorcycle helmet.

But, authorities said, there was no DNA — neither at the scene nor at VanCallis’s home — to connect him to the crime.

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At trial, the prosecutor slammed VanCallis’s helmet on the table.

“This helmet knocked her silly,” he told jurors, according to the Detroit Free Press.

The most damning testimony, it seems, came from VanCallis’s ex-girlfriend, who told police she saw him cleaning his shoes with hand sanitizer, according to the newspaper. She told authorities that she found human hair in his jacket pocket.

She also told them that VanCallis had told her: “I messed up. You need to stand by me.”

VanCallis, prosecutors said, asked his brother to delete the texts between him and his former girlfriend.

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“He cleaned off the DNA,” the prosecutor said. “He cleaned off April.”

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Cataldo, the prosecutor, also showed jurors animation using GPS data from a fitness app on the teenager’s cellphone that was laid over a Google Earth map. It showed the phone moving fast from the crime scene, which Cataldo said proved VanCallis had taken the girl’s phone and fled, according to MLive.

Cataldo said surveillance footage also showed a motorcycle zipping past a nearby house at the same time the phone did.

VanCallis’s attorney, Azhar Sheikh, insisted that there was no smoking gun.

“What counts is the evidence,” Sheikh told jurors, according to the Detroit Free Press.

He said the prosecution had “a whole lot of confidence in their lack of evidence.”

When the guilty verdict came down Monday afternoon, some people in the courtroom let out a gasp, according to local news reports.

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Others started to celebrate.

“Let me finish and then you can do what you want,” Macomb Circuit Judge Mary Chrzanowski told the court, according to MLive.

After the decision, Jessie Kanehl, who spoke for the victim’s family, said Millsap’s relatives were trying to find some closure.

“They are taking the time to digest this verdict,” she said, according to MLive.

But, she added: “I know you can never get total closure because April is not going to be here with us. She’s not going home with them today.”