Kimberly Saenz, originally born as Kimberly Fowler, was born in Fall River, Massachusetts. She went to Central ISD in Pollok, Texas, which is near Lufkin, Texas, for junior high and high school. Kim was a cheerleader during her junior high and part of her high school years. In her junior year, she became pregnant by her high school boyfriend and gave birth to her son the same year. After the birth of her son, Kim left Central High School.

Eventually, Kimberly earned her high school diploma or its equivalent and went on to study at Angelina College in Lufkin, Texas. She earned her vocational nursing license there. Kimberly then got a job as a nurse at a DaVita dialysis clinic. However, she had a troubled work history and had been fired from at least four healthcare jobs. One of these firings happened at Woodland Heights Hospital, where she was caught stealing Demerol (a pain medication) and cheating on a urine test.

Kimberly was married and had two young children. She struggled with drug dependence and used stolen prescription medication. In 2007, she was arrested for public intoxication and criminal trespass after a domestic dispute with her husband, although they later reconciled.

In spring 2008, DaVita's Lufkin clinic saw a strange increase in patients getting very sick during treatment. Paramedics had to come to the clinic 30 times in April, twice as much as the entire last year. One patient, Thelma Metcalf, had to go to the emergency room several times because she got too much of a blood thinner called heparin. Other patients had heart attacks, which was very unusual since dialysis patients rarely had such emergencies.

After two patients, Thelma Metcalf and Clara Strange, died of heart attacks on April 1, DaVita sent Amy Clinton, a clinical coordinator, to the Lufkin clinic. But the problems didn’t stop. Paramedics were worried and told their bosses at the Lufkin fire department, who then secretly asked state health inspectors to look into the clinic.

On April 28, 2008, while inspectors were at the clinic, two more patients, Marva Rhone and Carolyn Risinger, had severe drops in blood pressure. Patients Linda Hall and Lurlene Hamilton said they saw Saenz draw bleach into two syringes and inject it into Rhone and Risinger's dialysis lines. When Clinton asked Saenz about it, Saenz said she was cleaning an unused machine and used a syringe to measure bleach, which was against DaVita's policy. The bucket and syringes Saenz used tested positive for bleach. The police were called, and the clinic was closed for two months. Saenz was fired and later had her nursing license suspended. She then tried to work as a receptionist, breaking her bail conditions.

An epidemiologist from the Centers for Disease Control and Prevention (CDC) found that Saenz was present at every incident where someone died in April. Saenz's computer had searches about whether bleach could kill. When questioned, Saenz mentioned using bleach to clean lines before the detectives brought it up. She said she had to use a syringe to measure bleach because there were no measuring cups. Saenz was arrested for five counts of capital murder and five counts of aggravated assault with a deadly weapon.

Candace Lackey, a co-worker, said Saenz disliked several patients, all of whom either died or had emergencies. Another co-worker, Sharon Dearmon, said Saenz took a cigarette break after treating Opal Few, who then had an emergency, but Saenz refused to hurry back to help her.

Even with strong evidence and witnesses, police and prosecutors worried they didn’t have enough for a conviction because there wasn’t much research on detecting bleach in blood. Mark Sochaski, an expert, tested samples and found bleach in nine of them. He explained that bleach in the bloodstream caused the red blood cells to explode, leading to heart attacks and death.

On March 31, 2012, Saenz was found guilty of murdering five patients and injuring five others. She was sentenced to life without parole for the murders and three consecutive 20-year sentences for aggravated assault. The five victims were Clara Strange, Thelma Metcalf, Garlin Kelley, Cora Bryant, and Opal Few.

District Attorney Clyde Herrington believed there were more victims than the 10 known cases. The CDC linked Saenz to other health problems, but the police could only get medical waste from two weeks before April 28, 2008, so there wasn't enough evidence for more charges. During the trial, Thelma Metcalf’s daughter called Saenz a "psychopathic serial killer" and said she hoped Saenz would burn in hell. Saenz's appeal was denied. She is now serving her sentence at the Mountain View Unit in Gatesville, Texas.