Taking your questions one by one:
WOULD THE ELECTRICITY HAVE GONE OUT?
It's possible but unlikely. According to a number of sources,
including this Lab Safety document...
Safety in the Laboratory
...fibrillation sets in at around 100 milliamps of flow through the
body. Above around 200 milliamps, the heart is clamped so tightly that
fibrillation does not occur - but the victim will still die if not
found immediately, because breathing is impossible.
There would also be current flowing through the bathwater - an
informal discussion on this page estimates it to be around 120
Suppose the total current flow (body plus water) is 250 milliamps.
That's a quarter of an amp. A household fuse in a very old building
might be as little as 5 amps, but even so the electrocution current
alone isn't going to blow the fuse.
If, however, other appliances are operating that are near the fuse
limit, the electrocution current could take the total current above
the level that blows the fuse. That's probably what happened in the
situation described by pinkfreud-ga in the comments.
In a newer property, protection might be provided by a ground fault
circuit interruptor (or residual current device) in addition to a fuse
or circuit breaker, in which case the circuit should certainly go dead
in less than a tenth of a second (but in that case the victim would
Also bear in mind that most houses have more than one electrical
circuit. If the fuse blows on the circuit that powers the radio that
was dropped into the bath, it isn't necessarily going to blow the fuse
that powers the lights.
DANGER TO THE FIRST PERSON WHO HAS CONTACT WITH THE BODY
If the fuse has blown, the power is off and there is no risk to the
person who contacts the body (assuming the fuse is on the "live" side
of the circuit, and that the "return" or "neutral" side is close to
If the power is still on, and someone touches the body or puts their
hand into the water, they will get a shock. Provided there is no path
through their heart the risk will not be so high as for the person in
the bath. For example, if they are standing on dry flooring and put
just one hand into the water they are likely to survive, but if they
are leaning against a grounded metal object when they reach a hand in
they could die.
THE SCENE NINE HOURS LATER
If the bath plug does not make a good seal, the bath will have drained
dry. Otherwise, the victim's skin is going to look really wrinkled
from the prolonged contact with the water ("prunation"). Prunation
does not go away after death, even if the water is removed.
Rigor mortis (where the muscles become hard due to increased ATP and
lactic acidosis) will be near its peak.
Livor mortis will also be near its peak.
"During livor mortis, the body becomes distended and
skin colour progressively changes from green to purple
and finally to black. The dependent areas of the body
undergo this process first due to the pooling of blood,
and this is usually seen within 2 hours of death, with
the process of livor mortis reaching its maximum at
Wikipedia - Death
WOULD THE AUTOPSY BE ABLE TO RULE OUT A HEART ATTACK?
Certainly, yes. A "heart attack", or myocardial infarction, causes
scarring of the heart tissue which would be easily detected by the
Maybe you are using the term "heart attack" loosely, to include
cardiac arrest, in which case the question becomes more interesting:
"Ventricular fibrillation (VF) constitutes the most
common electrical mechanism in cardiac arrest, and
is responsible for 65 to 80% of occurences..."
Wikipedia - Cardiac Arrest
I'm not aware of a way the Coroner could easily distinguish between
fibrillation caused by an electric current, versus fibrillation
followed almost immediately by an electric current.
A research article mentions that, of six cases of death in a bathtub
with a hairdryer, none showed electrical burns (because the
electricity flow is distributed across a large part of the skin when
the victim is in a bath). Some victims showed petechial haemorrhages
which are assumed to be due to the combination of cardiac arrest and
Electrocution--autopsy study ... "electrical petechiae"
If cardiac arrest and muscle contractions the cause, the petechiae
might also be present at autopsy if the fibrillation occurred just
before the electrocution.
The forensic examination of the bathroom is likely to reveal some
clues. Perhaps there are some tiny chips where the radio banged
against a shelf or the edge of the bath on its way down, or other
clues as to how the appliance came to be in the bath.
Let me also refer to you a very extensive question and answer posted
to Google Answers in 2003:
"I'm working on a murder mystery, and I need to know
how the effects on the human body of electrocution
when an appliance is dropped in bath water are different
from the effects of electrocution when a person
comes into contact with power lines. During an autopsy,
could a medical examiner tell the difference and how?"
Forensic medicine electrocution
In his answer, tutuzdad-ga provided enough material about autopsies
that you could weave your story whichever way you wanted.
Good luck with your murder mystery!
Google Search Strategy:
electrocution "how much current" heart
Wikipedia - Electric Shock
Wikipedia - Ventricular fibrillation
Wikipedia - Myocardial infarction