Could a DNA sample taken 31 years ago solve the infamous yogurt shop murder case?

When four teenage girls were murdered in an Austin, Texas, yogurt shop in 1991, a heartbroken city was left searching for answers. No one imagined that more than 30 years later, the case would remain unsolved. 

But now, thanks to new advances in DNA technology, there is renewed hope that a piece of evidence collected from the scene on the night of the crime will be key to solving the case once and for all. "48 Hours" correspondent Erin Moriarty reports on the latest developments in "The Yogurt Shop Murders," reairing Saturday, August 27 at 9/8c on CBS and streaming on Paramount+.

On December 6, 1991, 17-year-old Eliza Thomas, 13-year-old Amy Ayers, and two sisters, 17-year-old Jennifer Harbison and 15-year-old Sarah Harbison, were found gagged, tied up with their own clothing, and shot in the head in an I Can't Believe It's Yogurt! shop in Austin. Whoever was responsible had also set the shop on fire, compromising much of the evidence. 

Eliza and Jennifer had been working at the yogurt shop that night. They were getting ready to close when Jennifer's sister, Sarah, and their friend, Amy, met them there to head home. Investigators believe at least two men entered the shop and committed the brutal crime. 

Gunshot wounds revealed two different types of guns were used — but there was scant other evidence at the scene, and debris from the fire complicated the early investigation. The Austin Police Department soon developed a task force dedicated solely to solving the crime. Government agencies, including the FBI, were called in to assist, but the case ultimately went cold until 1999, when four men, Robert Springsteen, Michael Scott, Maurice Pierce and Forrest Welborn, were arrested and charged with the murders.

The men were only teenagers at the time of the crime. They were first questioned just days after the murders when one of them, Maurice Pierce, was arrested at a mall not far from the yogurt shop with a .22 caliber gun — one of the same types of weapons believed to have been used in the killings. 

All four were released back then for lack of evidence, but in 1999, when a new team of investigators were tasked with taking a fresh look at the old case, they obtained confessions from two of the four men, Robert Springsteen and Michael Scott. Those confessions would later be called into question after the two recanted, saying they were coerced. 

Charges were ultimately dropped against Maurice Pierce and Forrest Welborn due to lack of evidence, and Robert Springsteen and Michael Scott were the only two to go on trial. The sole evidence against them were their own words. They were both convicted, but a few years later, their convictions were overturned on constitutional grounds. The Sixth Amendment gives defendants the right to confront accusers and in Scott and Springsteen's trials, their confessions were used against one another, but they weren't allowed to question each other in court.

Rosemary Lehmberg, the Travis County, Texas, district attorney at the time, was intent on retrying Springsteen and Scott. But before doing so, her office decided to take advantage of what was then a fairly new type of DNA testing called Y-STR testing. It was a way of searching for and extracting male DNA only. Y-STR testing was ordered on vaginal swabs taken from the victims at the time of the murders. By this point, investigators had come to believe that at least one of the victims had been sexually assaulted. As a result of the Y-STR testing, a partial male DNA profile was obtained from one of the girls, but to the surprise of the district attorney's office, the DNA sample did not match any of the four men who were arrested.

CeCe Moore, a DNA expert and genetic genealogist whom we interviewed for this week's "48 Hours," told correspondent Erin Moriarty that Y-STR DNA is a tool sometimes used in criminal cases. Moore explained it "can eliminate almost everyone. … Everyone but the suspect."

"If their Y-STR does not match, they did not contribute that DNA?" Moriarty asked Moore.

"Because of… where that DNA was found, yes, in this case, it's very important," Moore said.

Still, prosecutors were determined to retry Springsteen and Scott. But before doing so, they wanted to figure out who that mystery DNA belonged to. 

District Attorney Lehmberg says more than 100 men — such as crime scene investigators and personnel from the medical examiner's office who might have come in contact with the body and possibly been a source of contamination — were tested. It was all to no avail. In 2009, with no matches, the charges against Springsteen and Scott were dropped. After nearly 10 years behind bars, they were released, but not exonerated, leaving open the possibility they could be retried at a later time.

For years, officials kept trying to track down the source of the mystery DNA. Then, in 2017, an Austin police investigator searched a public online DNA database used for population studies to see if he could get a hit. Unbelievably, he did. It seemed to be the most promising lead in years, but there was a problem. The seemingly matching sample in the public database had been submitted anonymously by the FBI and had no name attached to it. When officials in Austin contacted the FBI in an effort to get a name, the FBI would not provide it, citing privacy laws. 

Frustrated, city officials reached out to U.S. Congressman Michael McCaul, who is from Austin, for help. McCaul pressed the FBI, and "48 Hours" has learned that in early 2020, the FBI agreed to work with the Austin Police Department to see if further testing could be done on that Y-STR DNA from the crime scene.

"48 Hours" has learned that initially, the sample from the crime scene was not very detailed and had only 16 markers, but more advanced testing in 2020 came up with an additional nine markers, bringing the total marker count to 25. However, this more advanced testing revealed that the sample from the crime scene no longer proved to be a match to the sample in the public DNA database. In a letter to Congressman McCaul obtained by "48 Hours," the FBI explained the new results "conclusively exclude the male donor of the FBI's sample … as such, the FBI Y-STR profile is not an investigative lead."

"And that was the greatest disappointment because we really thought we had it," Congressman McCaul told Moriarty.

Still, McCaul says that he and Austin officials will not rest until they determine who that DNA from the crime scene belongs to.

"We're waiting for… the DNA science to improve to then resubmit what we have left in the crime lab for further testing," McCaul said.

According to McCaul, some of the actual Y-STR DNA from the sample found on the victim in the yogurt shop case still exists.

"It's very limited and … that's why we're waiting for the science to improve on this, because there's very little left," he said.

With DNA research advancing so quickly, McCaul hopes that one day that sample of DNA obtained 31 years ago will finally solve the case.

"It's everything," he says.