AN OREGON MAN ACCUSED OF PUSHING HIS FIANCéE TO HER DEATH ON A HIKE TELLS PETER VAN SANT WHAT MAY HAVE HAPPENED THAT FATEFUL DAY, IN "48 HOURS: MYSTERY AT EAGLE CREEK"

Stephen Nichols Tells Van Sant: "Either I Pushed Her, She Jumped on Her Own Accord or She Slipped"

Saturday, March 17, 10:00 PM, ET/PT

An Oregon man accused of pushing his fiancée off a steep cliff during a hike nine years ago tells Peter Van Sant what may have happened that fateful day, in an unusual interview for 48 HOURS: "Mystery at Eagle Creek," to be broadcast Saturday, March 17 (10:00 PM, ET/PT) on the CBS Television Network.

"Either I pushed her, she jumped on her own accord or she slipped," Stephen Nichols tells Van Sant in a new interview with 48 HOURS about the case against him for the death of Rhonda Casto in 2009.

That question is at the heart of the investigation into what happened on March 16, 2009. Casto, a 23-year-old mother, set out for a hike with Nichols along the Eagle Creek Trail. On the way back, she left the trail, falling 150 feet before hitting solid ground. Nichols said he tried to resuscitate her. He called 9-1-1. Nichols later claimed Casto had been acting high, being silly and running on the slippery trail before she fell. Nichols initially wasn't charged with any crime.

Her family, however, didn't believe Nichols' version of what happened and continued to press sheriff's deputies to dig deeper. Meanwhile, Nichols started a new life raising their daughter and teaching English in China. The investigation went quiet until 2014, when a secret grand jury indicted Nichols for murder. He was arrested in San Francisco on a trip home the following year and charged with Casto's murder in Oregon. He pleaded not guilty.

What happened in the Columbia River Gorge that day?

In a new interview, Nichols tells Van Sant that Casto was asking strange questions as they headed to the hike.

"She said - 'If anything ever happens to me, would you promise to watch our daughter and take care of her?'" Nichols tells Van Sant. "And I go, 'What are you talking about?' She goes, 'I already know I'm gonna die by the age 25.'"

Pressed by Van Sant on what he saw when Casto fell, Nichols says, "Next question."

After she fell, Nichols maintains he climbed down the 150-foot cliff to reach her. He compares her to a wounded soldier. Asked whether Rhonda was alive when he got there, Nichols is even more elusive, and the interview takes a bizarre turn.

"Hmm, now we're - and that's the part I'm not going into," Nichols says.

"Did you put Rhonda out of misery that day?" Van Sant asks.

"Let me ask you," Nichols responds, "if you shoot your war buddy because you see how much pain he's in, is that murder?"

"What do you say?" Van Sant asks.

"I say no. Course not," Nichols says.

Julia Simmons, Casto's mother, believes Nichols killed her to collect on a $1 million life insurance policy. "People that have to make up lies are, you know, you can obviously tell that they're guilty," Simmons says.

What happened on the hike, and what did Nichols do? Van Sant and 48 HOURS investigate the case and the outcome that no one saw coming through interviews with Casto's family, friends, Nichols and others.

48 HOURS: "Mystery at Eagle Creek" is produced by Susan Mallie and Jennifer Terker. Michelle Fanucci is the development producer. Mike Vele, Ken Blum, Richard Barber and Diana Modica are the editors. Anthony Batson is the senior broadcast producer. Nancy Kramer is the executive story editor. Susan Zirinsky is the senior executive producer.

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