They are two of the most baffling criminal cases in decades—beauty queen JonBenét Ramsey, murdered in 1996, and college student Natalee Holloway, missing since May 2005. Both are still open cases, both are still being investigated, yet they've yielded precious few clues or new leads. Like thousands of other hard-to-crack crimes, they may never be solved. Here, six other haunting mysteries that continue to confound police

JASON ALLEN & LINDSAY CUTCHALL

The month before they were to be married in 2004, Christian missionaries Jason Allen, 26, and Lindsay Cutchall, 22, left the children's summer camp where they were counselors and headed off for a romantic weekend in Northern California. Four days later, on Aug. 18, the couple were found on a remote, fog-shrouded beach near the tiny town of Jenner. They were dead, shot in the head with a .45-cal. Marlin rifle while they slept. "This is a very troubling case," says Capt. Dave Edmonds of the Sonoma County Sheriff's Department. "They seemed to be upstanding individuals and very peaceful, not the type to put themselves in harm's way."

Three years and hundreds of interviews later, the mystery of who murdered the young couple remains, despite a $50,000 reward offered by Gov. Arnold Schwarzenegger. "This is a bad one," says legal commentator Daniel Horowitz. "In cases like this, if the murder is not solved within 24 hours through fingerprints and DNA ... it is going to be difficult to catch the killer." It hasn't helped that the murders took place in a rugged coastal area, where ocean winds and tides sweep the beach, possibly compromising the crime scene. "We don't know what might have been disturbed," says Edmonds, "or what potential evidence was lost."

In May of 2006, authorities released a photo of a necklace identical to the one Cutchall might have been wearing (but that was missing from her body), as well as details about four items found around the crime scene, including journal writings and a hat. They also disclosed that some DNA evidence had been found. Says Edmonds: "We are doing everything we can to move forward, even if it is just baby steps."

CHANDRA LEVY

She was last seen at her Washington, D.C., health club on April 30, 2001. But it wasn't until over a year later—long after the congressional intern's disappearance had become a full-blown scandal—that Chandra Levy's skeletal remains were found in the city's Rock Creek Park.

In an early interview with police, California Rep. Gary Condit reportedly admitted having an affair with her. (The married Condit never acknowledged the romance publicly.) From that point on, the police and the media focused relentlessly on his involvement, a rush to judgment that may have been one of the biggest hindrances to solving the case. "All of a sudden, Gary Condit became the only one they would consider," says a source close to the investigation. "We became fixated on him."

Yet Condit was never officially named a suspect; in 2002 he lost his bid for re-election. That year Ingmar Guandique, a Salvadoran national who was serving time for attacking two women in Rock Creek Park, came under suspicion, but police were hindered by a lack of physical evidence due to the severe weathering of Levy's skeletal remains (Guandique and his lawyer have said he had nothing to do with her death). Solving the crime is "almost impossible," says Joe McCann, a P.I. hired by the Levy camp. "The only thing that will break this case is a confession."

BOB STEVENS

On Sept. 19, 2001, shortly after the 9/11 attacks, Bob Stevens, a photo editor at the tabloid Sun, received a letter containing a white powder at his office in Boca Raton, Fla. On Oct. 5 he died in the hospital of anthrax poisoning. Over the next six weeks, other anthrax-laced letters showed up at NBC in New York, the New York Post and the office of then-Sen. Tom Daschle in Washington, D.C. In all, five people died of anthrax, including two postal workers. But no culprit has been found.

In August 2002 then-Attorney General John Ashcroft declared that bio-warfare expert Steven J. Hatfill, who had worked at an Army research facility at Ft. Detrick, Md., was "a person of interest" in the investigation. But Hatfill—who called himself "a loyal American" and said, "I have had nothing to do in any way, shape or form with the mailing of these Anthrax letters"—was never arrested or charged, and sued to clear his name. "It's an active case, and efforts to solve it have in no way been slowed," says Debra Weierman, a spokeswoman for the FBI, which still has 17 full-time agents on the case. Stevens's widow, Maureen, is hoping for a break. Says her attorney Richard Schuler: "She is standing fast in trying to get to the truth."

TUPAC SHAKUR
Slain in a drive-by gang shooting, the rap star remains the subject of conspiracy theories

On the evening of Sept. 7, 1996, after watching a Mike Tyson fight, Shakur, 25, was in the passenger seat of a BMW driven by Marion "Suge" Knight, the head of Death Row Records, on the crowded Las Vegas Strip. Suddenly a white Cadillac pulled up with four men inside. Shots were fired, and Shakur—who took four slugs in the chest—was fatally injured.

Out of those bare facts, many conspiracy theories have mushroomed. Earlier in the evening, Shakur's entourage had roughed up Orlando Anderson, a member of the Crips street gang. According to some witnesses, Anderson enlisted the Crips to carry out the hit and bragged the next day about being the triggerman. Police questioned Anderson but he was never arrested. (Anderson was later gunned down in L.A.) Some Shakur supporters accuse authorities of deliberately running a slack investigation and perhaps even having been involved in the hit. Others suggest that Knight, despite the fact that he was next to Shakur, could have been mixed up in the plot. Knight has repeatedly denied involvement. "The Crips shot Tupac," says Cathy Scott, the author of The Killing of Tupac Shakur, "but who was behind it?"

The chance that question will be answered seems remote. "The case is cold," says Scott. "Out of the four people in the Cadillac that night, two are dead. And I would imagine the other two are looking over their shoulders."

ANDY PUGLISI

She remembers people calling out his name—"Andy! Have you seen Andy?"—in the Lawrence, Mass., housing projects where they grew up. "And I remember someone saying he hadn't come home from the pool and thinking, 'Uh-oh, he's in trouble now,'" says Melanie Perkins, 40, recalling the terrible day in 1976 when her childhood sweetheart Andy Puglisi, 10, disappeared after they spent an afternoon together at the community pool.

Andy was never heard from again, but Perkins is still searching for him. Her documentary Have You Seen Andy? debuted on Cinemax this year and contains new clues, which led Perkins to believe a convicted rapist and pedophile, Wayne Chapman, killed Andy and buried him within two miles of the pool. (Chapman denies any involvement in Andy's disappearance.) Investigators have conducted three small digs but haven't been aggressive enough, says Perkins. She claims they never officially interviewed Chapman, who is in prison for raping two other Lawrence boys in 1975. "I'm frustrated," says Perkins, who wants a full search of the area around the pool. "Andy is still out there."

John Dawley, First Assistant DA for Essex County, says police have properly pursued leads and conducted searches based on specific tips. "But to pull apart a community wholesale without a tip or a corroborating reason," he says, "that we wouldn't do." Perkins, the mother of two young children and pregnant with her third, hopes the film pressures the FBI to step in and help find the boy she cannot forget. "I still have the faith I had as a little girl that he is going to be found," she says. "Andy needs to be brought home."

JACQUELINE LEVITZ
Signs of a struggle, blood on her bed—but no answer to who killed the Palm Beach socialite

After decades of decorating other people's dream homes, self-made millionaire Jacquie Levitz, 62, was ready to create her own. When her husband, Ralph Levitz, founder of the Levitz furniture chain, died in 1995, she bought a house in Vicksburg, Miss., and started renovating. Says her sister Gerri Brown, 71: "She was bubbling over with getting it done."

Levitz never lived to see that day. On Nov. 20, 1995, relatives found the door of her house ajar. Inside there were signs of a struggle, and a large bloodstain on her king-size mattress. But investigators mishandled what little evidence there was, contends Buddy Caldwell, the DA of neighboring Tallulah, La., who took an unofficial look at the case at the request of Jacquie's brother Don. "There was nothing nefarious about it," he says. "It was just that these were country law-enforcement people." One of them, Sheriff Martin Pace, defends the work of his department and the FBI: "This is still an open investigation. We have leads we are still following up on."