L5B - Saw marks in bones

Dismemberment of bodies, technical terms (kerf)

Why would someone dismember a body?

• Ease of transport

• Dispersal of body parts to more than one location

• Prelude to further processing

• Other behavioural attributes?

What is needed to cut up a body?

• Suitable tools​

• Somewhere to do it​

• Commitment/drive to do it​

• Specialist knowledge??

What is the easiest to cut through?

Long bone shafts

Can use knife/sharp blade to cut through flesh

What tool do you need to cut through bone?

Saw or similar instrument

(like butchers)

What requires detail knowledge of anatomy?

Cutting through joints

What is the structure of long bone shafts?

• Compact bone​ (forms the dense outer layer of the diaphysis, providing strength and resistance to bending forces. It contains osteons that support the bone’s weight-bearing capacity)

• Cancellous bone ​(is a lighter, less dense type of bone tissue found within the interior of bones)

What is the compact bone of the long shaft?

• forms the dense outer layer of the diaphysis, providing strength and resistance to bending forces. It contains osteons that support the bone’s weight-bearing capacity.

What is cancellous bone?

also known as cancellous or trabecular bone, is a lighter, less dense type of bone tissue found within the interior of bones.

primarily located at the ends of long bone.

What are the types of saws a pereptrator might use?

Hand saws - Likely to use saw blades designed for cutting wood, metal etc (unlikely to have surgeons or butchers saw)

• Power saws​- Reciprocating,​ Circular​, Band saws​

What are the types of power saws?

1. Rotary​

2. Reciprocating​

3. Band ​

4. Chain

What are the types of hand saws?

• Tenon saw​

• Crosscut saw

What is the most common saw for dismemberment?

hacksaw

What is a hacksaw?

• Used for metal​

• Easily accessible

• Replaceable blade​

• Can have different TPI or per 25cm​

• e.g. 18, 24 etc.

What is TPI and what does it indicate?

= teeth per inch

Higher TPI (e.g., 24 TPI) indicates a coarser blade, suitable for cutting harder materials like steel.

lower TPI (e.g., 14 TPI) is better for softer materials like brass or plastic.

What are key features of cut marks in bone?

• Cutmarks​

• Striations​

• Paint residues​

• Teeth per inch (TPI)​

What do all saw blades have?

have teeth which leave cut patterns in an object. ​

What is formed when a saw teeth cuts into bone?

Groove or kerf

What is a kerf?

the groove or slot left by a cutting tool, like a saw.

Walls & floor of cut

Provide most info

What does saw mark analysis involve?

examination of saw cut kerf floors and walls.​

What does floor contour include?

false starts and, occasionally, breakaway spurs. ​

What do kerf floors provide?

• most information about saw class (relationship of saw teeth to each other) ​

• includes set and number of teeth per inch (TPI) ​

What do kerf walls provide evidence about?

about teeth per inch, saw power, and the direction of cut. ​

When can knives be considered as saws?

when used in a reciprocating/sawing motion

What kerf shape does serrated knives have?

• lack saw set ​

• so they create a visibly narrow, ‘V’-shaped kerf walls and floors.​

• Serrated = has a saw-like edge with small teeth

What is a false start?

• cuts that do not completely separate bone​

• Will have kerf floor​

• Do not use term hesitation mark​

What are striations?

• Series of parallel lines on kerf caused by sawing​

What do saws consist of?

• row of teeth on a blade​

• These teeth will be set at an angle​

• Majority of saws cut on the push stroke​

• Some on pull stroke​

What are the teeth on a rip saw?

• Has chisel style teeth​

• Designed for “ripping” through wood​

• a cut made parallel to the direction of the grain​

• ensures that cut is wider than thickness of blade

What are the teeth on a crosscut saw?

• Has consecutive teeth filled at an angle ​

• Cuts rather than chisels through​

• Cuts across the wood grain​

What is a hacksaw classified as?

rip saw

What are the teeth on a hacksaw?

• ripped teeth​

• The set can be one of three types​

• Alternating (straight)​

• Most common​

• Raker ​

• Wavy ​

​

How would you technically describe a saw?

• Points per inch (per 25mm)​

• Teeth per inch (per 25mm)​

• Direction of cut ​

• push versus pull​

• Tooth profile (cross cut versus rip cut)​

• Width of cut (set)​

• Set pattern​