Decomposition happens when the absence of metabolism in the dead body causes cells to start dying and then they domino to cause the collapse of organs and body systems.

But if not for bacteria in our bodies, decomp would take much longer.

Essentially, on a normal day the average healthy human body has more bacterial cells on and in it than the total number of its own cells. But our bodies have checks to keep the numbers down (various forms of excretion, primarily, and our immune system) or to keep them contained to a particular area.

But after death all bets are off. It is a bacterial field day. There is nothing to contain the cells that can self-reproduce every 20 mins and, with unlimited access in all parts of the body to the entire body as an energy source, they get straight into massive and rampant reproduction. The bacterial frat party to end all parties. Thriving, changing, evolving bacterial processes long after the body is dead.

Thus, after death a body can potentially have more life in it than before.

So…if bacteria cobined to form super-organisms mabye they COULD create zombies from the living ‘sleeve’ of an ex-human being?

‘Trails of Evidence: How Forensic Science Works” is a The Great Courses DVD lecture series

Oxygen deprived blood is a dark red colour. When it’s well oxygenated it is a brighter/vibrant red.

Veinous blood may look blue because of light diffusion through skin and livor mortis (lividity) makes the pooling of blood in a dead body look purple/blue for the same reason. So you’d expect someone suffering from carbon monoxide poisoning (where the blood fills with carbon monoxide and so has no room for oxygen) to have deep, dark red blood, right?

Not so. Their blood is cherry red (and victims of carbon monoxide poisonings take on a cherry red skin colour making them easy to diagnose).

This is because haemoglobin binds much better to C0 than 0 so as far as the blood is concerned it’s fully loaded (and therefore bright red) but oxygen can’t get a look-in and so the cells start to die.

‘Trails of Evidence: How Forensic Science Works” is a The Great Courses DVD lecture series

Hollywood (and fiction to a certain extent) is partial to ‘pretty death’. Fictional characters are often conscious to their last breath, calm, and really only weakened by their impending death. They utter a few final words, or offer a hand-squeeze before their eyes either close or go glassy and their head droops. Perhaps a small puff of air.

All very…pleasant and contained.

Real death is never, ever pretty.

Because function leaves voluntary muscles in favour of more vital organs, the person’s jaw often goes slack and their mouth falls open, their eyelids flutter half open (because opening or closing them takes muscular effort), dehydration causes mucus to collect in a throat they can’t clear and creates a tortured ‘death raggle’ gurgle, the blood leaves the skin for the core leaving it blotchy or cold to the touch, the heart rate and respiration can double causing agitation, confusion, anxiety, hallucination and restlessness. And that’s all without unpleasant wounds to content with.

Other Hollywood myths about death

- The same abandonment of voluntary muscle control is behind the popular myth that a dead person will automatically void their bladder and bowel — they will if it’s very full but not because death causes some kind of surge of peristaltic activity. It’s just that the spincters that keep the bowel and bladder closed may relax when the body centralises its resources elsewhere and so anything waiting to come out…does. But someone with little or nothing in their digestive system to excrete won’t.

- fingernails and hair do not continue to grow after death because that would require metabolism. The scalp and the cuticles shrinks and pull back revealing more hair follicle or nail length which can look like growth.

- the person attending the crime scene is unlikely to be the person undertaking an autopsy. They are two distinctive roles with particular skill sets and are often used to verify each other’s findings and so having your coroner also be your crime scene death investigator is only a fictional convenience.

‘Trails of Evidence: How Forensic Science Works” is a The Great Courses DVD lecture series

• How coagulation works – when a blood vessel is damaged or exposed, the lining produces proteins which attract the platelets which make up 1% of blood. The platelets turn sticky and clag together to plug the small wound. Once they’re all wedged in there, they themselves form a protein which reacts in the bloodstream to form insoluble protein strands called ‘fibrin’ and these (like fibreglass strands) bond together to seal the wound.
• What makes a blood pattern? Blood generally has a fixed surface tension and a particular viscocity that makes it tend to cling to itself if left unchanged (kind of like the classic ball of mercury). But when gravitational forces or impact forces are sufficient, they can break blood’s inherent surface tension/viscosity and cause the blood to break into multiple droplets, the size and number of which create different patterns that forensic serologist can use to determine what happened at a crime scene.
• Types of blood patterns
  • Passive – generally the result of gravity (dripping, pouring, pooling, streaking) or transfer
  • Spatter – droplets scattered on a surface. They result from a force in addition to gravity (eg: blunt force trauma, gunshot, knife wounds etc)
  • Altered – changed through natural clotting, insect activity, mixing with organic material, attempted clean-ups or the presence of an obstruction that interferes with the natural patterning (eg: a void)
  • Sattelite droplets are secondary droplets caused when a passive droplet impacts something (like the floor) and spatters off
  • Cast-off is the particular name given to the droplets that have come off the weapon and not the victim. These are used to determine the minimum number of strikes and the order that the strikes happened.
  • All splatter is spatter but not all spatter is splatter – Spatter is the term used when droplets of blood are scattered on a surface by the forces of a crime/incident. ‘Splatter’ is a type of spatter but it is only one configuration of spatter
  • How to make blood that both looks and feels real – 500ml powdered milk, slowly add 325ml water (stir until smooth), 1.5ounces red food colour, 25 drops green, 5 drops blue.

‘Trails of Evidence: How Forensic Science Works” is a The Great Courses DVD lecture series

Flies might excite entymologists in the crime lab but they can seriously muck up the work of the serology team. Flies in a crime-scene can ingest blood and regurgitate it, which alters the composition and nature of the blood and thus the evidence.

They also excrete the blood in tiny amounts that, if there are enough flies, can replicate a kind of blood spatter and misdirect crime scene analysts.

‘Trails of Evidence: How Forensic Science Works” is a The Great Courses DVD lecture series

Just like there are bomb detection dogs and drug detection dogs, there are also arson detection dogs. Trained canine noses can sniff out tiny quantities of known accelerant hydrocarbons even after extensive burning. They are much quicker to use in the field than in-lab chemical tests.

Even though a regular fire itself can produce hydrocarbons that the dogs will detect, it doesn’t matter because forensic methodology allows for ‘false positives’ in the field that can be ruled out later in the crime lab. So it’s better to have a dog tell you there might be accelerant to be found (and end up being wrong) than have no dog and no idea to look for it.

‘Trails of Evidence: How Forensic Science Works” is a The Great Courses DVD lecture series

Every explosion (except for nuclear ones) have a positive and negative phase. As the name suggests, the positive phase happens as pressure, heat and noise moves away from the site of the explosion and sometimes this is known as the ‘shock front’.

But right behind that is the negative phase which is caused when the sudden outward moving of pressure creates a vacuum behind it that sucks gasses and debris back toward the explosion.

‘Trails of Evidence: How Forensic Science Works” is a The Great Courses DVD lecture series

Demographic-wise, the most dominant occupation of arsonists who light fires in order to be ‘heroic’ and discover them are:  Security guards, volunteer fire fighters, nightwatch personnel, baby-sitters and…wait for it…

…volunteer librarians.

I have *no* idea why librarians particularly love to watch things burn. You’d think flames would be the natural enemy of someone who loves books.

 ‘Trails of Evidence: How Forensic Science Works” is a The Great Courses DVD lecture series

• There are 250 million registered vehicles in the USA
• Statistically, city streets are safer (by far) than country roads, but this is the combined effect of lower driving speeds due to congestion and increased traffic control in cities, and the greater distances to hospital for country areas on fatalities.
• Economic losses from motor vehicle accidents are US$200 billion a year and 33% of those are accidents involving alcohol.
• In MVAs, drivers will typically under-represent own speed and over-represent other speed but that’s not necessarily attempts to be duplicitous, can be the distorted perception of reality.
• Equipment failure is a very small cause of vehicular accidents
  • 48% – collision with another vehicle
  • 26% – collision with fixed objects
  • 12% – pedestrian impact
  • 11% – ‘non collision’ impacts
  • 2% – collision with non motorised vehicles
  • 1% – collision with train
  • 0.2% – collision with animal

‘Trails of Evidence: How Forensic Science Works” is a The Great Courses DVD lecture series

The impact of two fully-loaded 767 aircraft slamming into New York’s World Trade Centre in September 2001 was not what cause the buildings to collapse.

It was the fuel spill.

Forensic engineers determined that the thousands of gallons of aviation fuel that spilled as the two planes exploded consecutively caused fires on six floors of Tower One and nine floors of Tower Two that incinerated everything on those floors over the next hour or so.  Contents, occupants, steel supports, concrete floors, everything. Smouldering like a furnace.

As a result, each building effectively had a six- or nine-story ‘void’ within one hour of the impacts and whatever structure did survive was in no condition to withstand the weight of the (respective) 19 and 11 floors above them. The sudden impact of those 19/11 floors hammering down into the void was what caused each tower to pancake and collapse.

Like taking the legs out from under a timber house. The combined weight of the whole thing dropping was way too much for the rest of the building to withstand. Even though they’d technically withstood the impact of the planes.

‘Trails of Evidence: How Forensic Science Works” is a The Great Courses DVD lecture series