Provo • As she walked in the moonlight through a snow-covered hillside outside Eureka in December 2017, Morgan Lewis knew something was very wrong.

Her boyfriend, Jerrod Baum, engaged in a casual conversation with two teenagers — was charming, even — but 17-year-old Brelynne “Breezy” Otteson and 18-year-old Riley Powell weren’t there because they wanted to be.

She said Baum had tied them up and he was marching them out into the West Desert. He caught the couple at his home, visiting Lewis. She wasn’t supposed to have male friends, Lewis testified Wednesday in a Provo courtroom.

As they walked, Lewis recalled that Breezy talked about being allergic to the sage brush and asked for Baum to untie her hands because they were going numb.

"No," Baum told her, "We're almost there."

He stopped in front of an open mine shaft and that’s when Lewis thought that she might die that night.

"I realized even if we listened," she testified, "it wasn't going to end well."

Lewis, who also has gone by the name Morgan Henderson, told a harrowing tale from the witness stand Wednesday of how she watched her then-boyfriend brutally kill the two teens. She testified during a preliminary hearing for Baum, who is charged with aggravated murder and other crimes.

The woman took long pauses as she recounted how Baum forced her to her knees in what she described as an "execution style" pose. Breezy was pushed down to her knees as well.

"It felt like we were an audience," she said as she described how Baum then forced Riley to stand in front of them.

Lewis was scared, and heard Breezy next to her whimpering and crying. At one point, she remembers holding the girl's hand.

“Riley asked if he could kiss his girlfriend,” Lewis testified.

Lewis said she looked on as Baum began hitting Riley over and over as he called him names. She realized when she heard a gurgling noise and Riley cry out, "I'm dying!" that her boyfriend was stabbing the teenager.

Riley fell to the ground, Lewis testified, and Baum kept stabbing him until the gurgling noises stopped. He waved at the teen and said, “Goodbye, Riley, you piece of s--t.”

Baum turned to Lewis and Breezy, the woman testified. As Breezy cried next to her and swore to Baum she wouldn’t tell anyone about what she just saw, Lewis said she felt then that he was going to kill them both.

But Baum went behind them, held Breezy in his arms and shushed her. “It’s OK, darling,” he told her, according to Lewis, as he rocked her.

Lewis then remembers feeling a warmth on her leg, she said — it was Breezy’s blood.

Baum had slit her throat.

Lewis said she stayed on her knees as she watched her boyfriend pick up Riley’s body and throw it in the open mine. He then scooped up Breezy and dumped her body down the hole as well.

She cried as Baum began trying to cover the blood — "There was so much blood," Lewis testified — by pushing dirt around.

Her boyfriend knelt in front of her and told her she needed to pull herself together, Lewis testified, threatening to harm her and her son if she didn’t help him clean up after the killings.

“He looked manic,” she testified. “He looked overjoyed. He’s got this huge grin on his face like he’s enjoying himself. He did later laugh about it and said that it was like lambs to the slaughter. They didn’t even fight.”

(Rick Bowmer | AP file photo) In this April 7, 2018, file photo, a reward poster is shown at a funeral service for Brelynne "Breezy" Otteson, 17, and boyfriend Riley Powell, 18, in Eureka, Utah. Prosecutors say an enraged man killed the teenage couple after they visited his girlfriend despite his warning her not to have male visitors. He dumped their bodies in the mine shaft, where they remained for nearly three months before being discovered in March.

After the killings, Lewis testified that they hid Riley’s Jeep and bleached and burned their clothes. They scrubbed their bodies with bleach. Baum stashed the knife in an oil barrel, and hid Riley’s keys in random dirt piles.

And when the police came to question the couple after Riley and Breezy were reported missing, Lewis said she lied. A Facebook message showed that Riley had agreed to come to her home with Breezy that Dec. 29, but she said they never showed up.

The guilt gnawed at Lewis as weeks dragged on — two families asking for the public to help them find the missing teens. She couldn’t live with the secret, she testified, but was terrified that Baum would hurt her or her son.

So she got a gun and some mushrooms and decided to die by suicide. But before she could go to the mountains where she had planned to kill herself, she was already high and got pulled over for speeding by a police officer who took her to jail.

She decided then to tell investigators what she saw.

"I wanted those families to have closure," she testified. "I wanted them to know what happened."

In late March 2018, Lewis led police to the mine shaft and she told them that the young couple had come to their house in Mammoth, smoked marijuana and talked for a while before Baum came home and saw Riley and Breezy about to leave.

Lewis testified that Baum had been a controlling partner who forbade her from having male friends or people over at their home.

Lewis believed Riley and Breezy had left but then Baum led her outside, where she saw the teens tied up in the back of Riley’s Jeep, she told police. Charging documents say the teens were bound at their hands and feet, and their mouths were duct-taped.

Baum drove Lewis and the young couple to the abandoned mine shaft known as Tintic Standard No. 2 before allegedly killing Riley and Breezy and dumping their bodied into the 1,800-foot shaft. The bodies landed on a ledge about 100 feet down. An autopsy report showed that Riley had been sliced and stabbed several times by a sharp object, according to testimony, and his throat had been cut. Breezy’s throat had also been cut.

During cross-examination, Baum's defense attorney attacked Lewis' credibility — including challenging her memory that the teens' hands were bound in the front. When their bodies were pulled from the mine, authorities discovered their hands were tied behind their backs.

Lewis also has a history of mental illness, including a condition that causes her to hallucinate and see things that aren't real.

She had agreed to cooperate with authorities and testify against Baum as part of a plea deal, after she pleaded guilty to 10 counts of obstructing justice for lying to police as they tried to investigate Riley and Breezy’s disappearance. She is now serving a three-year sentence in the Utah County jail.

Testimony is expected to continue Thursday in Baum's case. A judge will then decide whether there is enough evidence to move the case forward to trial.

Baum could face the death penalty for his alleged crimes.