The Ohio teenager who will be sentenced Monday after she was convicted of intentionally crashing her car at 100 mph had an increasingly toxic relationship with her boyfriend, who died in the wreck, prosecutors and family members said.

Mackenzie Shirilla, 19, was found guilty of 12 counts last Monday, including four counts of murder, in the July 2022 crash in Strongsville, Ohio, which killed her boyfriend, Dominic Russo, 20, and his friend Davion Flanagan, 19.

Prosecutors argued at the four-day trial that the couple fought and that Shirilla made violent threats — including once threatening to crash her car with Russo in it, which she ultimately deliberately did to end their tumultuous relationship.

“We put plenty of that sort of evidence in front of the judge,” Tim Troup of the Cuyahoga County Prosecutor’s Office told NBC affiliate WKYC of Cleveland after the verdict. “There is no doubt that this happened because of the relationship with Dominic, and the defendant’s intent was clearly to end that, and she took everybody that was in the car with her.”

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During the trial, security video of the crash played in the courtroom — showing her vehicle zoom on a street and crash with a roar into a building, with no signs of slowing down.

The crash happened around 5:30 a.m. July 31, 2022, when Shirilla accelerated her Toyota Camry into the Plidco Building in the Cleveland suburb of Strongsville. (via WKYC)

A certified forensic mechanic testified that her car’s event data recorder showed that moments before the crash, the accelerator pedal was being pushed down at full capacity with no application of the brake, WKYC reported.

Shirilla faces a maximum sentence of life in prison, without eligibility for parole for 32 years, the Cuyahoga County Prosecutor’s Office said.

Despite his heartbreak, Dominic Russo’s father told NBC News on Friday that he doesn’t support Shirilla’s spending her life behind bars.

“It’s horrible for everybody. Yeah, I lost my son, it’s harder on our family, but I don’t want the rest of her life ruined, too. It isn’t going to make me feel any better,” he said. He called her “a kid” who “did a damn stupid thing.”

Frequent break-ups and threats

Shirilla and Russo had been dating for three or four years, Russo's family members said. She had spent a majority of the relationship living with Russo at his home, prosecutors said in Cuyahoga County court filings.

Russo’s mother testified in court that he and Shirilla fought and that threats were made, and his brother, Angelo, testified that the couple broke up often.

Dominic Russo. (via WKYC)

“I witnessed a lot of negative behavior from her to my brother, and that just kind of pushed away as a big brother figure, because she just wasn’t fair to him,” Angelo Russo said.

Christine Russo, Dominic's older sister, 34, said she didn't see the fights in the couple's relationship but heard some details from Dominic’s friends.

“From what I heard from his buddies and people very close in their age, not that they saw [the crash] coming, but it wasn’t a surprise to a lot of people based off her behavior and how she was,” she said.

"You would never think in a million years, nobody ever would have thought that this would happen," she continued. "I think everybody says that when somebody's in a domestic violence situation or if they have an abusive partner, you just don't see that from the outside; it happens behind closed doors."

Davion Flanagan. (via WKYC)

Flanagan's father wrote on Facebook that his son Davion was just “an innocent passenger looking for a ride home."

Troup, one of the prosecutors, told WKYC: “He was friends with Dominic, and Davion was just cargo. He was just a suitcase in the backseat in the defendant’s mind.”

Two key incidents

At the trial, prosecutors highlighted two incidents they claimed showed Shirilla’s threatening and violent behavior.

On July 17, 2022, just two weeks before the fatal crash, Shirilla was driving on Interstate 71 with Russo as a passenger when she threatened to crash the car, apparently upset over a disagreement they had had, according to a prosecutor’s filing.

Russo called his mother by phone and asked to be picked up during the disagreement. One of his friends ended up going to get him. The friend was on the phone with Russo when he heard Shirilla say: “I will crash this car right now.”

When the friend pulled up to pick up Russo, he found Shirilla’s car pulled over on the side of the road with the passenger-side door open. The friend saw her "striking Dominic with both of her hands. Dominic then exited the vehicle and left,” the filing said.

During another conflict in July 2022, Russo recorded Shirilla making threats toward him.

Videos from Russo’s cellphone revealed that the two got into an altercation, and Shirilla was heard “repeatedly degrading Dominic, threatening him, and damaging his property,” the court filing said.

Dominic wasn’t comfortable letting her inside his home, the filing said, and he was heard trying to calm Shirilla down, to no avail.

Shirilla instead was heard banging on the house door demanding to be let inside and calling him “degrading and highly inappropriate names.”

She threatened to key his car and break off the door handle, verbally counted down multiple times to force him to let her in and said, “You’re gonna come open this door right now or there’s gonna be a serious f---ing problem.”

He ultimately stopped recording and called his mother for help.

Shirilla’s defense argued that the situation wasn’t one-sided and that she and Russo mutually fought with each other. Her attorneys also argued that whether she crashed the car intentionally couldn’t be determined.

'U are the last person to deserve this'

After Russo’s death, Shirilla flooded his online obituary with photos of the two.

In a post on Aug. 24, 2022, she shared a photo of the couple at Universal Studios, with the caption: “I miss you nug. I still feel like your just going to walk in the door any second. I miss your laugh your perfect smile.”

“God u are the last person to deserve this you had such a perfect life ahead of you … I wish I told you all this more. Please wait for me.”

Throughout August she posted multiple pictures of the two together, including prom photos.

Crash was 'methodical, deliberate, intentional'

Shirilla was found guilty of four counts of felonious assault, two of aggravated vehicular homicide, one of drug possession and one of possessing criminal tools, in addition to four counts of murder.

Cuyahoga County Common Pleas Judge Nancy Margaret Russo gave a blistering rebuke of Shirilla's actions when she announced the verdict, calling Shirilla "literal hell on wheels."

"Her actions were controlled, methodical, deliberate, intentional and purposeful. This was not reckless driving. This was murder," Russo said.

The crash happened around 5:30 a.m. July 31, 2022, when Shirilla accelerated her Toyota Camry into the Plidco Building, a large brick building at the intersection of Progress and Alameda drives in the Cleveland suburb of Strongsville, police and prosecutors said. (via WKYC)

"The video clearly shows the purpose and intent of the defendant: She chose a path of death and destruction that day," she added.

She said Shirilla drove on purpose around 5:30 a.m. — an hour when not many witnesses would be around, along a path she didn’t routinely use but had visited a few days before.

"She had a mission, and she executed it with precision. The mission was death," Russo said.

This article was originally published on NBCNews.com