William Alfred Holloway's health was improving – at least that's what his family was told by staff at the Veterans Affairs hospital in Clarksburg, West Virginia.

"The nurse told us his numbers are great," his daughter, Karen, said.

But the next morning, the 96-year-old Army veteran was dead.

Holloway's death, which has not been previously reported, was the first of three suspicious deaths in three days. All the patients stayed in the same third-floor unit of the Louis A. Johnson VA Medical Center, according to their families. All died after unexplained drops in their blood sugar levels.

Authorities are investigating about 10 suspicious deaths at the hospital amid concerns the veterans were targeted. Five victims have been publicly identified, including two that have been ruled homicides.

Two other deaths have been ruled undetermined. In the other case, the veteran was cremated before a medical examiner could examine the body.

Though it can be hard to detect a pattern across a hospital, the deaths of three patients in three days – all of whom stayed in unit 3A – is "a huge red flag," said Beatrice Yorker, a nurse andcriminal justice professor at California State University-Los Angeles. She has written extensively on serial killingsin the health care industry.

A string of suspicious deaths:What we know about veterans who died at the Clarksburg VA

The string of deaths has gripped this small town in north-central West Virginia and drawn the attention of lawmakers on Capitol Hill.

Everyone has the same question: How could this happen?

"The concentration and frequency of death is really deeply, stunningly disturbing," said Sen. Richard Blumenthal, D-Conn. "It indicates a pattern reflecting premeditation."

Blumenthal, a member of the Veterans Affairs committee, told USA TODAY that Senate hearings may be convened to determine whether a hospital employee was responsible for the deaths and whether the Department of Veterans Affairs failed to protect patients.

He stressed that no crimes have been proved, but he noted investigators identified a "person of interest."

The VA said the person of interest was "removed from their position in Clarksburg" and is not a current employee.

"There is a need for accountability, not only for the individual culprit who may have been responsible," Blumenthal said, "but also for the VA. It has to provide an explanation. We will seek an explanation."

Clarksburg VA spokesman Wesley Walls reiterated an earlier statement that hospital leadership notified authorities “immediately upon discovering these serious allegations,” and they put “safeguards in place to ensure the safety of each and every one of our patients.”

Walls referred further questions to the VA Office of Inspector General, which is working with the FBI and Department of Justice on the investigation. Spokespeople for the inspector general and Justice Department did not provide any updates.

‘He didn’t just die a normal death’

Karen Holloway said she couldn't remember why her father was admitted to the hospital in April 2018. She remembers feeling relieved the night before he died, when a nurse told her he was doing better.

For months, Holloway’s family believed he had died of sepsis, a life-threatening condition caused by the body's response to an infection. In fall 2018, federal investigators told the family several patients had died under suspicious circumstances – and Holloway was one of them.

Karen Holloway said the agents told her they had received an anonymous tip "that someone was injecting these soldiers" with insulin. They showed the family a chart of Holloway's insulin level just before he died, his daughter recalled.

"It was off the charts. More than what he needed," Karen Holloway said. "He didn’t just die a normal death."

Though some diabetics rely on insulin to control their blood sugar, an unneeded injection can lower it to a dangerous, even fatal, level.

Holloway died April 8, 2018. The next day, another patient who stayed in unit 3A, Felix Kirk McDermott, died after his blood sugar suddenly dropped. He had been admitted to the hospital three days earlier and was getting better, his family said.

On April 10, George Nelson Shaw succumbed two weeks after his blood sugar plummeted to a dangerously low level without explanation.

"It started going back up, and then it crashed again," his wife, Norma, said. "After that, he just went downhill."

The first victim:Authorities investigating 10 suspicious deaths at VA hospital, including one ruled a homicide

McDermott and Shaw's bodies were exhumed and examined at Dover Air Force Base. A medical examiner discovered insulin injection sites on both bodies. Neither man was diabetic.

Their deaths were ruled homicides.

Holloway was a diabetic, and he did take insulin to control his blood sugar, his daughter said. His autopsy revealed several injection sites consistent with his treatment.

But the medical examiner noted that before Holloway died, he suffered a "prolonged episode" of severe low blood sugar that lasted for 30 hours.

"There is no natural cause" that would explain why Holloway's blood sugar dropped so severely and was resistant to treatment, the medical examiner wrote. “This episode is strongly suspicious” for unprescribed administration of insulin, he concluded.

He ruled the death "undetermined."

When should hospitals investigate patient deaths?

Investigators have made no arrest in the Clarksburg case and divulged no evidence. It is unclear why none of the early insulin deaths triggered a review that might have identified a pattern of possible homicides.

An inspector general review of the hospital, conducted in May 2018, found that hospital officials reported no major incidents of patient harm or danger during the previous 20 months, which includes the time period of the deaths under investigation.

The hospital started looking into the deaths in June 2018, according to a timeline provided by the office of Sen. Joe Manchin, D-W.Va. That's when VA doctors informed the hospital's quality management team that eight patients had experienced unexplained, dangerously low blood sugar.

Most health care systems have strict policies designed to identify and review incidents in which patients are harmed or die unexpectedly. In the VA, “sentinel events” require an analysis by medical experts, who report their findings to headquarters in Washington.

Yorker and other experts contend that medical serial killers are a known phenomenon in the health care industry and require systems to detect and prevent harm.

Yorker co-wrote a study identifying 131 cases worldwide since 1970 in which medical providers were prosecuted for murder or assault on patients, mostly using medications in hospitals.

That includes Orville Lynn Majors, who was convicted in 1999 of murdering six patients at an Indiana hospital and is suspected in dozens of other deaths.

In 2004, Charles Cullen, a nurse, pleaded guilty to killing 29 patients at medical facilities in New Jersey and Pennsylvania.

In those cases and others, hospitals were sued by victims' families for wrongful deaths and were sanctioned by state regulators, according to published reports.

Elizabeth Yardley, a criminology professor at Birmingham City University in England, has studied cases in which patients were killed in hospital settings. She said it's common for killers to become more brazen as time passes from their first killing.

"The killings will get closer together toward the end," Yardley told USA TODAY. "You will often find there is a large gap between the first and the second murder, a slightly smaller gap between the second and the third. … When they are caught, it is to such an extent that it can’t be ignored."

'They killed my father, didn't they?'

Two weeks before Holloway died, on March 26, 2018, another veteran who stayed in the same unit succumbed in similar circumstances.

His name was Archie Edgell, 84, an Army veteran. He was admitted to the hospital because of problems associated with his dementia.

He was diabetic, though he had been given insulin by relatives at home and was not prescribed insulin at the hospital, said Dino Colombo, his family's attorney.

Within 48 hours of being admitted, Edgell's blood sugar level plummeted. Hospital staff gave him glucose to try to bring it up.

Hypoglycemia requires immediate treatment when someone's blood sugar drops to 70 mg/dL, according to the Mayo Clinic. Two days before Edgell died, his blood sugar was 25 mg/dL, Colombo said.

“There’s no reason for his blood sugar level to have dropped like that,” Colombo said. “He had a number of health issues, but there was nothing that should have killed him.”

Investigators with the VA's Office of Inspector General showed up at the home of Edgell’s son in West Virginia in fall 2018, around the same time they contacted Holloway’s family.

Colombo recounted Steve Edgell's reaction: “They killed my father, didn’t they?”

An autopsy conducted in December 2018 found four injection sites on Edgell's arms and thighs that tested positive for insulin.

“These findings are strongly suspicious for unprescribed ... insulin administration during his hospitalization,” the medical examiner wrote. The manner of death was ruled "undetermined."

Edgell, whose death was first reported Thursday by MetroNews in West Virginia, served during the Korean War and was stationed in Germany. He worked as a mechanic in the Army. After his service, he worked as a water commissioner in a small town near Clarksburg for 20 years.

His wife of more than 60 years, Kathleen, died in April without knowing what happened to her husband.

Holloway spoke little of his service

William Holloway served in the Army during World War II, but he often changed the subject when questions about his service came up, Karen Holloway said.

After he was discharged, he lived with his wife, Malinda, in Fairmont, West Virginia, where he worked for the U.S. Postal Service. They raised two daughters and had three grandchildren. Malinda Holloway died in 2011.

As a postal worker, Holloway was credited by police for preventing an elderly woman from being scammed out of her savings. William Holloway recounted the decades-old incident to a newspaper reporter in 2015.

He was on his route when a woman told him she’d been directed by a bank official to withdraw money from her account to help catch bank employees who had been stealing from customers.

“I could see through that story right away,” William Holloway told the paper. “I called the police.”

Two men were arrested for trying to defraud the woman.

Holloway loved to hunt, fish and golf. Karen, the older of his two daughters, went with him on fishing trips when she was a child even though she hated it. “I just wanted to be with Daddy,” she said.

Karen Holloway said she was just beginning to accept her father’s death when investigators contacted her and asked if they could dig up his body. It was a tough decision.

“Is this the right thing to do?” she remembered asking herself. “And then I thought he would be saying, ‘You better fight and exhume me.’ He would’ve gone through with it.”

Holloway was reburied after another military funeral.

“We’ve had two funerals for Daddy,” Karen Holloway said, her voice trembling. “Two funerals.”

Contributing: Ken Alltucker, Tom Vanden Brook and Dennis Wagner