Vsauce! Kevin here, with a serial killer who may very well have murdered hundreds. Her
systematic killing spree went undetected for years because suspicion just wasn’t enough.
What finally brought her to justice was… math.
In the United States, the most dangerous place you can go is… the hospital. Yes, doctors
and nurses save lives literally every single day, but medical error is a significant cause
of death. No matter how hard we try, tragedies happen -- and by definition, everyone in a
hospital is already sick with something. But murder isn’t an accident, and a nurse in
Massachusetts was straight-up killing patients… to impress a guy.
Kristen Gilbert was a nurse at the Veterans Administration Medical Center in Northampton,
Massachusetts. She was popular with co-workers. She’d go out clubbing with them in Boston
to blow off steam, and even threw baby showers. She also seemed to be really good at her job
-- it felt like she was always around to save the day in an emergency. She appeared to be
the perfect nurse.
But Gilbert was around so often when patients died that other nurses jokingly referred to
her as the “Angel of Death.”
It seemed like the Northampton hospital had a lot of unexpected deaths… but a VA investigation
found that the hospital’s rate of deaths was in line with similar VA hospitals.
So. Case closed, right? WRONG.
Doctors and nurses weren’t convinced, but there were no witnesses who saw Gilbert actually
do anything suspicious to patients. There wasn’t any evidence. But there was data.
Here’s a question: how often did patients die when Gilbert was on the floor, compared
to when she wasn’t? Was there a correlation between her presence and patient deaths? And
if so… was it just an unlucky coincidence? Or was she killing people?
The first analysis can be expressed visually -- this graph shows patient deaths in the
hospital ward between 1988 and 1997 broken down into 3 shifts: day, evening, and overnight.
The 4pm - midnight evening shift stands out as having the most deaths, and Kristen Gilbert
worked the evening shift.
But that doesn’t hold for every year. 1988 and 1989 don’t match up with the 6 years
that follow it. There weren’t that many deaths, and they were pretty evenly distributed
throughout the day.
Kristen Gilbert didn’t start working on the ward until 1990.
Okay. Okay. What about the really high number of deaths during overnight shifts in 1990?
That’s an outlier in this whole data set -- Gilbert worked evenings, but when she started
in 1990, she worked the overnight shift.
HUH. HUH. HUH.
But this graph is still not proof. Variation in human outcomes is tremendous, whether it’s
education or physical fitness or death. It’s totally possible that Kristen Gilbert was
present during a statistical blip. It’s possible there’s some nurse out there working
on a floor where patients never seem to die, like some kind of Angel of Life! Just ask
Brandon Mayfield whether coincidences happen. Or the FBI.
Dr. Stephen Gehlbach, who is now Dean Emeritus of UMass-Amherst’s School of Public Health,
ran the numbers. He looked at 1,641 nursing shifts over the period of 18 months leading
up to staff taking their concerns to hospital management. There were 74 deaths during those
shifts -- which is a death on 4.51% of all shifts, or .045 deaths per shift.
Kristen Gilbert worked 257 shifts during that 18 month period. With .045 deaths per shift,
we’d expect her to be present for about 11 or 12 deaths -- about 1 every 6 weeks on
average.
15 or 16 deaths when you expect 11 or 12 could be an unlucky statistical anomaly. She was
there for 40. FORTY! A patient died on over 15% of Gilbert’s shifts. What are the chances
of THAT? We’ll find out in a second.
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Okay. So, what are the chances? Literally 1 in 100 million -- and maybe even LESS.
In the handwriting analysis I did of Sylvia Howland’s will, Hetty Green’s forgery
matched on way too many points to chalk it up to a crazy coincidence, 1 in sextillions.
Gehlbach calculated p-values to estimate the chance of Gilbert’s nursing death-rate at
less than 1 in 100 million… but we know from the Sally Clark trial that a probability
like 1 in 73 million isn’t necessarily what it feels like it is. Correlation isn’t causation.
Maybe her patients were just sicker than normal.
This time, that uncertainty was okay -- it was enough for the grand jury to proceed.
A grand jury doesn’t have to determine guilt or innocence the way a trial does. They just
decide whether the evidence is compelling enough to proceed with criminal charges. They
did.
Again. There wasn’t proof. But the math gave enough context to the suspicions of the
Veterans Administration, hospital management, and Gilbert’s co-workers to proceed with
charges -- but how was she killing these people? And WHY?!?
Prosecutors alleged that Gilbert had injected patients with epinephrine – which you probably
know as adrenaline, which sped up their hearts and caused cardiac failure. Adrenaline is
untraceable, but the hospital found that it had a lot of epinephrine go missing during
Gilbert’s employment. And some of the patients -- like Henry Hudon, who was relatively young
and a paranoid-schizophrenia patient, weren’t likely to have 3 heart attacks in one night
without something artificially causing it.
But… why would a professional mother of 2 in suburbia become a deranged super-villain?
Well… She seemed to have delusions of grandeur in which she herself put patients in critical
condition and then heroically tried to resuscitate them. She had a history of manipulative behavior,
mental illness, and abuse of patients -- as a home care aide in the 1980s, she scalded
a mentally disabled child with hot bath water on purpose.
Kristen Gilbert may have been unhinged -- but she was also in love. Obsessively in love.
Every time a patient coded, hospital policy mandated that a police officer engage in CPR.
In late 1995 and early 1996, the same police officer responded to every single cardiac
arrest that Gilbert reported: James Perrault, Kristen’s boyfriend. The man she left her
husband and two children for. Witnesses noticed her touching Perrault affectionately during
resuscitation efforts and wiping his sweaty brow. Court papers show that "One witness
will testify that he observed Gilbert playing `footsie' with Perrault during the middle
of a code.” Gross.
Perrault ended the relationship, and Gilbert was angry. On a phone call from a psychiatric
facility, she confessed to him by saying, "You know I did it. I did it. You wanted to
know. I killed those guys." Perrault immediately went to the authorities, so… she called
in a bomb threat to the VA hospital where they worked.
Decades of troubling behavior culminated in a systematic killing spree that allowed Gilbert
to be the focal point of crisis after crisis. Staff testified about her access to the adrenaline
that induced cardiac events, and doctors testified that the unexpected excess deaths were often
relatively healthy, middle-aged men. The same pattern just kept happening.
Kristen Gilbert was convicted of 4 murders and 2 attempted murders -- and the bomb threat
to a federal facility. It’s possible -- and probable -- that she was involved in many,
many more patient deaths that weren’t the accidents they seemed to be, but prosecutors
couldn’t prove it. She could’ve faced the death penalty, but a compassionate judge
and jury sentenced her to a life in prison without the possibility of parole -- plus
20 years.
The mathematical analysis that was so critical to Gilbert’s downfall wasn’t even used
at the trial. The trial judge ruled that the statistical evidence was prejudicial, as it
likely wouldn’t be understood by the jury as NOT being iron-clad numerical proof of
her guilt.
I’ve shown that math can be an incredible asset in court… or that it can turn innocent
people into criminals. We’re getting used to scientific and mathematical evidence, like
DNA and forensics, determining guilt or innocence -- but the reality is math and science don’t
have to do all the work.
Dozens, and maybe hundreds, of veterans are alive in Massachusetts because of a bar graph.
Math and science don’t always have to put out the fire. Sometimes all they should do
— and all they need to do — is sound the alarm.
And as always, thanks for watching.