(CNN)Investigators knew his name. Now they needed his DNA.
When Raymond Rowe, known professionally as "DJ Freez," finished a DJ set at an elementary school in Lancaster, Pennsylvania, last month, he didn't know undercover officers were watching him.
Investigators had long tried to solve the 25-year-old slaying of a young schoolteacher. Her case had been cold for decades, but recent improvements in genetic science led investigators to Rowe.
But Pennsylvania State Police officers needed one more thing: a recent DNA sample from him to make sure they had the right guy. And they soon got one, all thanks to some chewing gum and a water bottle.
Rowe, 49, was arrested Monday and charged with criminal homicide in the 1992 slaying and sexual assault of 25-year-old Christy Mirack. Before the DNA testing, Rowe wasn't a suspect, even though he had lived just four miles away from Mirack when she was killed.
"This killer was at liberty from this brutal crime for longer than Christy Mirack was on this earth alive," said Lancaster County District Attorney Craig Stedman at a news conference Monday. "This case means a lot to us."
Investigators never gave up searching for Mirack's killer. To understand what went down, let's rewind a little.
A slaying without a suspect
On December 21, 1992, Mirack never showed up to teach her sixth-grade class at Rohrerstown Elementary School. Concerned, the principal went to check on her at home and found the front door ajar.
When he walked inside, he saw Mirack dead on the floor. She was wearing a winter coat but was naked from the waist down. Her face was badly bruised.
Investigators believe she was on her way to work when she was sexually assaulted, beaten and strangled to death. There was evidence of a struggle.
"It would appear from the scene that she fought for her life," Stedman said at the news conference.
Police were able to collect DNA evidence from the perpetrator's semen but couldn't find a match in any database.
"Her dream in life from early on was to be a schoolteacher,'' her brother, Vince Mirack, told CNN eight years ago. But soon after she reached her goal, ''it was taken away from her," he said.
The case puzzled investigators for decades and went cold.
How DNA cracked the case
In 2016, Mirack's case was transferred to the District Attorney in Lancaster, Pennsylvania, and in time, they too ran out of leads and suspects. But they didn't want to give up hope.
At long last, a breakthrough came this year when the DA's office contracted with Parabon NanoLabs, a DNA technology company, to perform genetic testing on DNA samples collected from the crime scene in 1992. When the samples were first tested, they were put into a criminal database, but there was no match.
What Parabon does is use genetic geneology to compare DNA samples in massive public databases to find people with enough genetic similarity to be family members. The science was also used to catch the Golden State Killer and has solved many other cold cases recently, including one last week in which a WWII veteran was found to have stolen the identity of an 8-year-old and another just days ago in which DNA on a napkin helped solve the killing of a 12-year-old girl.
"Parabon was really our last shot, and little did we know at the time that it's turned out to be our best, and led us to today," Stedman told reporters.
Information from the DNA at the scene was uploaded into a database named GEDmatch, which can show the amount of shared DNA between two people, according to Steven Armentrout, president of Parabon NanoLabs.
Systems like GEDmatch are valuable because members of the public voluntarily send their DNA to the database, making it an important resource for genealogists to make inferences about family trees and suggest potential suspects to investigators.
The evidence from GEDmatch pointed to Rowe's family. From there, it didn't take long to narrow it down to Rowe.
Rowe, a DJ, owns a business called Freez Entertainment. According to the bio on his company's website, he "started as a break dancer in the early 80's then started DJing shortly after and soon became a popular house party DJ in the mid 80's." The website also says that "there are many DJ's who follow in the footsteps left by DJ Freez, however there is only one recognized leader in the Central PA area."
Even though Rowe had lived in Lancaster County for many years after Mirack's death, he was never on authorities' radar before DNA testing pointed to him, Stedman said.
Going undercover to track a suspect
Stedman said that although Parabon played a crucial role in finding a suspect for the case, their suggestion wasn't enough on its own. Investigators had to be sure it was Rowe.
To do that, officers from the Pennsylvania State Police went undercover at a school function in May where Rowe was playing music. The undercover officers observed him with gum and a water bottle and later collected them as samples.
The results were damning.
After comparing DNA found on the gum and bottle to samples taken from Mirack's body in 1992, the probability of the perpetrator being anyone except for Rowe was approximately one in 200 octillion from the Caucasian population, according to Stedman.
"An octillion is one thousand trillion, trillion," he said. "That's a number with 27 zeroes behind it."
There are only about 7.6 billion people on the planet. Investigators were convinced that after more than two decades of searching, they'd likely found their guy.
The next step: Understanding why
Stedman says that while this looks like the conclusion to Mirack's case, in some ways, it's really just the beginning.
"We've known about the brutal death of Christy Mirack, but the arrest is when it starts," he said. "We've got a long road ahead of us but we're going to do it together."
Although investigators now have a suspect for Mirack's death, they still don't understand why it happened. To continue the investigation, the District Attorney has turned to the public to ask if anyone has information about how Mirack and Rowe knew each other.
"This is by no means a closed investigation and we encourage people if there is anything that they know, that we would like to hear from them," Stedman said.
Stedman says that genetic genealogy might be the ke