At another time in her life, Denise Heap might have tossed aside the insurance forms listing the drugs prescribed to her mother.

The "explanation of benefits" forms came like clockwork and didn't require any action on her part.

But Heap was worried about her mother, Joyce, who was in the end stages of Alzheimer's disease. Her health had inexplicably declined in the Los Angeles-area nursing home where she'd been living. So in April, when a thick envelope arrived from her mother's Medicare drug plan, Heap scrutinized it.

What she found was frightening: Her 77-year-old mother was receiving a raft of medications Heap had never seen before.

As Heap began Googling the drugs, she realized something was drastically wrong. Either her mother was being given expensive medications for conditions she didn't have — such as breast cancer, asthma, emphysema and high cholesterol — or something sinister was going on: Someone was using her mother to steal drugs.

"I flipped," Heap said. Medicare's prescription program, known as Part D, paid for more than "$10,000 worth of meds" in just three months, she said.

She first called Medicare to report her suspicions, she said, then the insurance company that managed her mother's Medicare drug plan. Neither, she said, seemed very concerned.

"I was like, ‘No. No. No. You have to understand. I am trying to help you guys,'" she said.

Soon, Heap became convinced someone had stolen her mother's identity while she was living at a nursing home run by an Armenian couple. The couple kept moving the location of the nursing home. And Heap believed they had been over-sedating her mother with high doses of antipsychotics, inappropriately treating her blood pressure and allowing bed bugs to feast on her.

"I knew something crooked was going on," said Heap, 59, who, with her mother, had co-founded a Holocaust education nonprofit in the 1990s to document stories of German resistance to Hitler.

Frustrated, Heap called Los Angeles County sheriff's Sgt. Steve Opferman, head of a task force specializing in prescription drug fraud. As soon as Heap began describing what had happened, Opferman said he knew her mother had been caught up in a fraud scheme involving Armenian organized crime.

Opferman and other investigators say criminals wager that patients and their families will not be like Heap. They bank on the fact that their victims —Medicare beneficiaries — will be too old or too sick to review insurance forms summarizing the medications and services billed in their names. And they count on the tendency of busy family members to give such forms a cursory glance, if that.

"Suffice it to say most people don't pay attention, let alone know what they're looking at," Opferman said.

But Heap's case, and others like it, shows the important role patients and their families can play in uncovering fraud within Part D. The program now covers 36 million seniors and disabled people and fills 1 in 4 prescriptions nationwide. Last year, it cost taxpayers $62 billion.

In an earlier report, ProPublica found that Medicare's system for pursuing such fraud is so cumbersome and poorly run that schemes can quickly siphon away millions. Tips such as Heap's can come into private insurers, which run Part D for Medicare, to contractors hired by Medicare to spot fraud, or to the U.S. Department of Health Human Services inspector general, which investigates health care fraud. But only a small percentage of cases funneled through this chain are prosecuted.

Reporters, using Medicare's own data, were able to identify scores of doctors whose prescribing within the program followed known patterns of fraud: the cost of doctors' prescribing jumped dramatically — in some cases by millions of dollars — from one year to the next and they chose brand-name drugs that scammers can easily resell.

Some doctors claimed that they — like some of the patients involved — were unwitting victims of identity theft. In other cases, federal investigators found, the doctors were paid for writing bogus or inappropriate prescriptions.

In a response to these findings, a Medicare official said more focus has been placed on fraud detection within Part D.

The drugs listed on Joyce Heap's explanation of benefits forms are those most-desired in such fraud schemes. They included the asthma drugs Spiriva and Advair Diskus, for which her insurance plan paid nearly $270 a month each, the cholesterol drug Crestor, which cost nearly $170, and the antipsychotic Abilify, for which the plan paid about $920 for a 30-day supply.

Opferman said Heap's call launched an investigation that uncovered a large Part D scheme allegedly connecting the owners of the nursing home to a North Hollywood pharmacy operation, including evidence that other residents' identities were used. A September search of the pharmacy where Heap's mother's prescriptions were filled found evidence that drugs were being relabeled or repackaged for resale, he said.

The doctor who prescribed the drugs has denied prescribing the vast majority of them, Opferman said. The case is now part of an ongoing investigation by California's Department of Justice and his group, he said.

Opferman said investigators might never have known of the scheme without Heap's tip.

Joyce Heap didn't live long after her daughter unearthed the problems.

She improved briefly after moving to a new nursing home, where a doctor reduced her psychiatric medications, Denise Heap said. But she died of a heart attack on April 21.

In the months following her mother's death, Heap said, she sent letters alerting Medicare and her mother's insurer to the possible fraud. In July she wrote, "Please note that 100% of the prescriptions charged in April 2013 … are FRAUDULENT."

Heap said she is "outraged" Medicare didn't follow up and ask detailed questions about her allegations. In fact, it was either her insurer or Medicare — she can't recall which — that recommended she call the local sheriff if she was worried.

"I would have thought immediately they would have gotten on it," she said.

But Heap said she is mostly tormented that she didn't know such fraud schemes existed — and that elderly people like her mother could become prey.

"It's a hard thing to live with," she said, tearfully. "I feel like I failed."