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Eighteen-year-old Denise Pflum had a bright future ahead of her. She was a star athlete. A gifted artist. Ranked at the top of her class. And she had dreams of becoming a scientist.

“She had everything going for her,” Denise’s mother, Judy, told Dateline. “If she were here today, she’d be working on a cure for cancer. Or, well, maybe even a cure for this coronavirus. She just wanted to help people.”

High school graduation was just around the corner and in March 1986, Denise had already been accepted to Miami University in Ohio where she planned to major in Microbiology. She was hoping to go on a track scholarship. Denise also played volleyball, basketball, and softball.

She lived at home in Connersville, Indiana, with her parents, Judy and David, and her younger sister, Jenny, who was a high school sophomore.

Prom was just a month away for the Connersville High School senior, and Denise had already picked out the perfect dress during a weekend trip to Indianapolis.

“She talked her dad into taking her when he picked her up from her trip,” Judy said. “I remember being upset because I didn’t get the chance to shop for a dress with her. You always think you’ll have more time, but you never know.”

Denise never got to wear that dress to her prom. On March 28, 1986, she vanished.

“It was Good Friday,” Judy said. “And I remember it being a really beautiful day. Warm.”

Students were off that week for Spring Break, which meant getting to hang out late with friends. Parties. Many of the parties in that area were held on someone’s farmland -- with a bonfire at the center of it all.

Denise had recently broken up with her boyfriend of three years, her mother said. “She started to be more social. She was hanging out with her friends more. Dating,” Judy said.

So Denise went to a party the night before Good Friday. A small gathering soon turned into several hundred teenagers. Denise returned home that night – but forgot her purse.

The next day, Denise wanted someone to go with her back to the party site to look for the purse. But none of her friends could go, and her sister had softball practice and couldn't go.

“We’re not sure why she didn’t want to go alone,” Judy said. “She was fearless. Ever since she was a child. So for her to be uncomfortable to go back to the site of the party is unnerving. Something wasn’t right.”

But Denise got into her cream-colored 1981 Buick Regal and headed out to the party site. She never made it. According to the family, the tenant of the farmland told them he never saw her return on that Friday.

“We do not believe that she ever went back to that area – something or some person interrupted that opportunity to do that," David Pflum told NBC affiliate WTHR in 2018. "We knew right away that something was wrong because she had never been out without our knowledge about where she was going to be. When the time unfolded into the next day and the subsequent next days then we knew we really had a problem.”

Judy told Dateline she saw her daughter briefly on Friday.

“I worked at a bank about a quarter of a mile away from our house,” Judy said. “We got three hours off that day for Good Friday, from 12 noon to 3 p.m., so I was home a little after noon.”

When Judy got home, Denise told her the plan to go back to the party site to look for her purse.

“That was the last time I ever saw my daughter,” Judy said. “And before I went back to work that day, I had a gut feeling. Something did not feel right to me.”

Not even an hour after Denise left the house, Judy said a distant cousin of Denise, who had gone to school with her, returned the purse to Judy at their house.

“But there were no cell phones back then,” Judy explained. “No way to call Denise and let her know.”

When Denise did not return home that evening, her family reported her missing.

“We thought maybe she had a car accident,” Judy said. “We drove all over the county looking to see if her car was in a ditch somewhere.”

The next day, a farmer from Glenwood, Indiana reported that Denise’s Buick Regal, which was registered to her parents, was abandoned alongside Tower Road, a gravel lane east of Glenwood. He said the car had been there since between 12:30 p.m. and 1:15 p.m. the day she went missing, but he told authorities he initially thought it belonged to mushroom hunters.

The car, which was locked, was in a rural area near a barn across the county from where Denise’s family lived and about three miles away from the party site. Her family said there was no reason for her to be in that area.

Since the Pflum family did not live within the city limits of Connersville, Denise’s case went from the city police department to the Fayette County Sheriff's Department.

Fayette County Sheriff Joey Laughlin told Dateline they are continuing to investigate the case and follow up on new leads.

Sheriff Laughlin said the case has been a difficult one because any evidence that might have been found on or around Denise’s car has been lost or destroyed over the years.

“It’s very difficult. We’re trying to complete a puzzle -- a puzzle where a lot of the pieces are missing,” Sheriff Laughlin said.

Sheriff Laughlin, who has been the sheriff for six years, was just seven years old when Denise disappeared.

“This case has been the great mystery of Fayette County for 34 years,” Sheriff Laughlin told Dateline. “But there is constant activity in this case. We haven’t given up.”

The Indiana State Police has also been brought in to investigate.

According to State Police Detective Sergeant Scott Jarvis, the agency collected DNA samples from the family, along with a DNA sample from a baby tooth belonging to Denise. It has been put into the National DNA Database System.

The evidence has been resubmitted to the Indiana State Police lab to check for any new results given the advances in technology over the years, but those tests did not provide any new clues.

Sheriff Laughlin confirmed there are several persons of interest in the case, but adds there is not enough evidence to charge anyone.

“We believe more than one person is involved -- by statements they’ve made or by their relationship to Denise,” Sheriff Laughlin said.

Denise’s case is also being worked on by someone else.

Stacy Reese has made it her mission to find out what happened to Denise. She was only three years old when Denise vanished and grew up in the same town. Her mother babysat both Denise and Jenny when they were children. Her father was a volunteer firefighter and assisted the search parties in the days following Denise’s disappearance.

Today, Stacy is a police detective in Vincennes County, but volunteers her services to help the Pflum family and has become their spokesperson.

“It has always been a part of my life. If you live in this area, you know about Denise and you know her story. It’s part of you. It's part of all of us,” Stacy told Dateline. “Denise’s story is why I became a cop.”

Stacy has been following every tip and lead she receives and in 2018, started a Facebook page “Justice for Denise Pflum” to raise awareness of the case.

“This case is solvable,” Stacy said. “All you need is one person. One person to come forward with the information we need. The missing link that completes this puzzle.”

Stacy told Dateline she’ll continue to fight for justice for Denise and closure for the family, which has become like her own.

Judy echoed Stacy’s sentiments, and added that they are forever grateful for her.

“We’re so blessed to have her in our lives,” Judy said. “She’s part of our family, really. She always says I remind her of her late grandmother. That means a lot. We have that bond. And now she’s part of Denise’s story.”

Now in their 70s, Denise’s parents told Dateline they are worried they'll never know what happened to their daughter.

“Our only hope is keeping her story alive,” Judy said. “And that it one day leads to justice for our girl.”

The Pflum family is offering a $25,000 reward leading to the location of Denise and information leading to the arrest of the person or people responsible.

If you have any information on Denise’s case, please call the Fayette County Sheriff’s Department at (765) 825-1110 Ext. 604 or the Indiana State Police at (765) 778-2121.