(NewsNation) — More than 12 years after Indiana University student Lauren Spierer went out for a night with friends, her whereabouts are still unknown.

It’s been over a dozen years since Spierer’s parents heard their daughter’s voice. The grief is so paralyzing that her parents have stopped doing interviews about their daughter.

Instead, the family has hired private investigator Mike Ciravolo. The former NYPD detective led the Zodiac Killer task force in the 1990s and is the senior investigator at his firm, Beau Dietl and Associates.

“I saw it on every news channel,” Ciravolo said of the case.

Spierer disappeared after a long night out with friends on June 3, 2011. That night, she followed a common path for IU students living downtown.

She started at her apartment in Smallwood Plaza. Spierer texted her boyfriend, Jesse Wolff, saying she had plans to go to bed.

But she didn’t.

Instead, Spierer went out to Kilroy’s Sports Bar with friends, using a fake ID to drink. Witnesses said Spierer was visibly intoxicated when she left the bar, forgetting her shoes and phone.

She wasn’t alone when she left. Spierer was with Corey Rossman, who was seen on unreleased surveillance video walking with Spierer back to her apartment building.

At one point in the video, Spierer trips and falls in an alley.

When they arrived at Spierer’s building, Rossman was confronted by others who knew her.

“They saw she was in bad shape to travel, and they were trying to do the right thing. They suggested to Corey, ‘Hey, you know she’s in bad shape. Why don’t you just make sure she gets back to a room down the hall?'” Ciravolo said.

According to police and reporting from NewsNation affiliate WXIN in Indianapolis, Rossman resisted, and one of the men hit him in the face.

Then, Rossman and Spierer took a five-minute walk to Rossman’s apartment at the 5 North Townhomes.

Based on what the men told authorities, Rossman’s roommate, Mike Beth, saw they were both drunk. He helped put Rossman to bed after he threw up and tried to convince Spierer to stay on the couch.

Beth said he was studying at the time and asked his neighbor, Jay Rosenbaum, to help with Speirer. Rosenbaum tried to convince her to stay, but she ultimately left the apartment barefoot with no phone.

Rosenbaum said he saw Spierer walk to 11th Street and College Avenue.

It was the last time anyone saw her.

The next day, Spierer’s boyfriend reported her missing when no one could get in touch with her. But after that, Ciravolo said Wolff and the other boys Spierer was with that night became uncooperative.

“After Jesse reported her missing later that afternoon. Jesse was like, ‘She’s dead. I know she’s dead.’ Well, how do you know she’s dead? So that’s Jesse Wolff,” Ciravolo said.

Multiple news reports said Wolff helped look for Spierer in the initial days after her disappearance but then quickly left town.

Wolff also passed a privately administered lie detector test, though he declined to take one administered by the police.

Ciravolo said he only spoke to Wolff once.

“He lets his father run interference for him. I would uncover some information and then I would get a call from Alan Wolff, Jesse Wolff’s father: ‘Where are you going with this? What are you doing? Could you tell me what’s going on?'” Ciravolo said.

He said he’d talked to all the men with Speirer that night except for Rossman.

Rossman called the police on Ciravolo and his team when they went to try to question him at his apartment.

“Cory Rossman has not been cooperative with us from day one,” Ciravolo said.

Rossman didn’t respond to NewsNation either despite multiple attempts to reach him and the other men.

The only one to respond was Mike Beth, who said he had “nothing to add.”

Talking to witnesses has been a major challenge for Ciravolo, who was hired in September 2011, three months after Spierer vanished.

“June to September is an eternity when you have this type of case. The earlier you can get involved, the better,” Ciravolo said.

On top of that, Ciravolo said police in Bloomington, Indiana, have also been resistant to working with him.

“We were told in no uncertain terms by (Police Chief Michael) Diekhoff that he would not be interested in having help; he would certainly not be willing to share any information with us. And he was also reluctant to accept any information that we had to offer to him,” he said.

Ciravolo was critical of the initial police investigation. So was the community. NewsNation affiliate WXIN in Indianapolis reported that some neighbors said they hadn’t seen police or been questioned by them for 10 days, even though police records indicated they spoke to “nearby residents” the day after Spierer disappeared.

When NewsNation asked for an interview, the Bloomington Police Department said it is policy not to do interviews.

In a statement, the department said that “the investigation remains very active” and “over the last three to four years, investigators have received over 800 tips and executed at least 10 search warrants.”

As for Ciravolo, he believes three things could have happened to Spierer.

One possibility is an opportunistic attack from someone who took advantage of Spierer’s drunken state. Another is her boyfriend doing something to her out of jealousy.

Ciravolo’s third theory has to do with Spierer’s health.

“Lauren, who had a bad heart and may have been overserved that night, could have passed; her heart could have given out while she was in their apartment in Rosenbaum’s apartment, and that they concealed her body,” he theorized.

Spierer had a heart condition called long QT syndrome, which can cause dangerous heart arrhythmias and in some cases may lead to cardiac arrest.

Spierer was also petite, just 4 feet, 11 inches tall and weighing only 95 pounds.

“It leads one to believe that perhaps they acted in concert in some way, shape or form and perpetrated a criminal act,” Ciravolo said.

However, the men and their parents have maintained they did nothing wrong and have cooperated with police. None of the men have been named as suspects.

In an article in the Journal News, Rossman claimed the Spierers and reporters were harassing him and threatened to call his lawyer.

NewsNation spoke to a former friend of Rossman’s, who met him in the fall of 2011 after Spierer disappeared. She asked to remain anonymous.

“So I hung out with him quite a bit,” the friend said. She said she often went to parties with Rossman and Rosenbaum.

“They were always super nice to me, like they were never disrespectful, creepy, anything,” she told NewsNation.

NewsNation asked Ciravolo what he would say if he could talk to Rossman now.

“Be a man. Put on your big boy pants and come forward. And if you’re telling the truth, you have nothing to fear,” he said.

Spierer’s parents have repeatedly asked anyone who knows anything to come forward. Her mother posted a statement online on the most recent anniversary of her disappearance.

“Twelve years you have kept your secret. Twelve years we have continued our search. I write today as a reminder that we will never stop,” she said.

For Ciravolo, every reminder is a chance to spark someone’s memory and uncover new information.

“Someone may see something, see this interview, and pick up a phone and they have real solid information, or maybe have a finally have a conscience and come forward with that information,” he said. “When you’re a detective, you can’t have any preconceived notion. You have to let the chips fall where they may and the facts lead you.”