The Fairmount Park rape suspect lived in the woods behind a school in Mayfair

Fifty feet behind the athletic fields of Mayfair’s Lincoln High School, in a dense wooded section of Pennypack Park, Elias Diaz tried to make himself something of a home.

The 46-year-old set up a portable charcoal grill. Hung tattered clothes from tree branches. Left cans of beer and old food wrappers on the ground, and stacked black trash bags on top of one another, some of them overflowing with junk.

He also stored a few more curious items: a child’s green scooter, leaned against a tree, and a worn stuffed animal a few feet away.

The makeshift homestead was hard to access — only reachable through holes in a chain-link fence near the school grounds, and cut off from the larger section of the park by Pennypack Creek.

But this week, the plot of dirt that Diaz had sought to carve out for himself became part of a high-profile criminal investigation. Police over the weekend arrested Diaz and charged him with attacking park-goers with a machete last month — and then, in a startling turn of events, came to believe he was also the so-called Fairmount Park rapist, a long-sought assailant who had brutally attacked women in parks, one fatally, nearly two decades ago.

The case against Diaz came into sharper focus Wednesday, when he was arraigned on charges including murder and rape for one of those crimes: the assault and fatal strangling of 30-year-old Rebecca Park in 2003. Diaz was jailed and held without bail as authorities said their investigation into his older crimes — which is centered on new forensic technology, including genealogy and DNA — is ongoing.

Still, a host of questions remained unanswered, including where Diaz was, and what he may have done, in the years since 2007 — the last time police say they received a report of a crime matching the pattern of the so-called Fairmount Park rapist. At least until last month, when Diaz allegedly began slashing people in Pennypack Park.

Authorities said they weren’t even sure in recent months that Diaz was alive. They’d identified him as a suspect in the old rape cases back in the spring thanks to genealogy analysis, but when they tried to locate him, family members across the mainland United States and Puerto Rico said they’d long been estranged from him and were not sure where he was. Some believed he might have overdosed or died, police said.

Several agencies that work with people experiencing homelessness said Wednesday that they didn’t know Diaz, or didn’t have a record of having interacted with him. He was arrested twice over the last 15 years, but for comparatively minor offenses, police said — and long before detectives had identified him as a suspect in the rapes.

Deputy Police Commissioner Frank Vanore said Wednesday detectives planned to reevaluate any open sexual assault or homicide cases that might seem to fit the pattern of Diaz’s alleged attacks. Still, Vanore said, even though Diaz’s identity had been a mystery until recently, his DNA had been in a national database for the last 20 years because it was collected from the victims in the sexual assaults. And Vanore said he’s not aware of any cases that had a DNA link to Diaz since 2007, when he allegedly raped and robbed a 29-year-old woman in Pennypack Park.

That doesn’t rule Diaz out as a suspect in other crimes; not all rape victims come forward to report them to police, and it may not be possible to collect DNA in cases reported days or weeks later. Vanore acknowledged it would be unusual for a repeat assailant to simply retreat from criminal activity for 15 years only to reemerge and begin attacking strangers in parks again by slashing them with a knife.

Still, he said: “We just don’t know where he was, and he’s not really telling us.”

“It really is bizarre,” Vanore added. “He’s on a bike in Pennypack Park, 20 years later ... kind of doing the same behavior.”

Diaz’s alleged attacks began in 2003, police said, when he attacked three women in a span of six months — a string of crimes that generated huge amounts of publicity and left some women fearful of walking alone.

In the second of those attacks, Diaz allegedly raped and strangled Rebecca Park. The 30-year-old student at the Philadelphia College of Osteopathic Medicine went for a jog around 4 p.m on a wooded trail near her home. She didn’t return, and her body was found four days later, partially undressed and in a shallow grave about 30 feet from the Fairmount Park trail.

In 2007, police said, Diaz raped and robbed his fourth victim, a 29-year-old woman in Pennypack Park.

DNA from the victims and the way the attacks unfolded led police to believe they were committed by the same person. But for years, they were unable to identify the potential suspect, beyond releasing sketches and general descriptions of what he may have looked like.

Then, in 2021, police used DNA analysis to create a new series of sketches, showing him as he might have aged, and released them to the public. Investigators also sent the DNA to a genealogy lab.

Ryan Gallagher, a police department forensics analyst, said that process led detectives and FBI agents to investigate links to nearly 1,000 members of a broad family tree that included Diaz. And Vanore said that as the potential matches got whittled down and pointed more directly toward Diaz, officers and federal agents traveled to places including Puerto Rico to try to find him.

Tips varied in quality and substance, Vanore said, and officers were generally stumped on his potential whereabouts.

Then, in November, a man began slashing people in Pennypack Park.

Starting on Nov. 22, police said, an assailant in the park began wielding a large knife against passersby, ultimately attacking three sets of people within three days. Police released information to the public and asked for tips — and on Dec. 17, an 8th District officer responded to the park for a call about a man riding a bike with a machete. The officer found Diaz with the knife and arrested him, and he was arraigned Monday on counts including aggravated assault and taken to jail.

Behind the scenes, Vanore said, investigators familiar with the rape cases quickly came to realize that Diaz had the same name as the suspect from the genealogy analysis.

On Tuesday, detectives obtained two DNA samples from Diaz, records show, and a forensic analysis showed a direct match between Diaz and the DNA recovered from one of the women raped in 2003.

Detectives also surveyed the woods of Pennypack Park on Tuesday afternoon and found what they believe was his encampment. They seized two bicycles for evidence. Much of the rest of Diaz’s ramshackle living area was left behind. It was not clear how long he had been living there.

By late Tuesday afternoon, officials held a press conference announcing their discovery, and prosecutors approved charges related to Park’s murder.

Diaz was arraigned Wednesday morning and jailed to await a preliminary hearing. He did not have an attorney listed in court documents.

Authorities have not yet charged him with the other rapes, but said their investigation is ongoing.

Attempts to reach Diaz’s alleged victims, including the surviving relatives of Rebecca Park, were unsuccessful Wednesday.

John Darby, the retired commander of the police department’s special victims unit, said the case was one of the most sobering of his career — and one that had stuck with him.

Although he is now a civilian, Darby attended Tuesday’s news conference and spoke from the podium about what it meant to him and other investigators.

“When you get cases like this,” he said, “they haunt you.”