Blood Spatter Analysis - Determining area of origin from impact stains.

Summary

This instructional video demonstrates the process of determining the area of origin from blood stain patterns, a technique used in forensic science. The presenter uses an impact spatter created by striking an object with a hammer to illustrate how blood disperses in a fanning pattern. Key steps include selecting and measuring various stains with a digital caliper, calculating angles with a scientific calculator, and using strings and a protractor to triangulate the point of convergence. The method helps estimate the location and height of the impact, providing valuable insights for crime scene investigations.

Takeaways

• 🔍 The video demonstrates how to determine the area of origin using blood stain patterns, specifically with impact spatter.
• 👨‍🔬 An impact spatter occurs when blood is forced out due to an impact, such as hitting an object with a hammer.
• 📏 To analyze the spatter pattern, one must measure the angles and distances using tools like a digital caliper and a magnifying glass.
• 📝 It's essential to select a variety of well-formed stains from different areas of the pattern to ensure a comprehensive analysis.
• 📐 The shape and angle of the stains are crucial; oval-shaped stains with an impact angle of 60 degrees or less are preferred for accurate measurements.
• ⭕ The stains should be numbered and their width and length measured to calculate the impact angle using the inverse sine function.
• 📊 The angles obtained from multiple stains should be similar; any significantly different angle may indicate a measurement error and requires re-evaluation.
• 📍 The point of convergence is identified by drawing lines through the center of each stain, which helps in pinpointing the area of origin.
• 📏 Strings or dental floss can be used to determine the height of the impact point by aligning them with the calculated angles.
• 📐 A protractor is used to set the correct angle for the strings, which are then attached to the point of convergence and extended to estimate the height.
• 📝 The process involves both mathematical calculations and careful observation to ensure the accuracy of the area of origin determination.

Q & A

What is the main topic of the video script?

The main topic of the video script is determining the area of origin using blood stain pattern analysis.

What type of spatter is required for area of origin analysis according to the script?

Impact spatter is required for area of origin analysis.

What is the significance of measuring the angles of blood stains in this process?

Measuring the angles of blood stains helps to determine the direction of the impact and contributes to finding the point of convergence, which is essential for identifying the area of origin.

What tools are suggested for measuring the blood stains in the script?

A digital caliper and a 10 times magnification magnifying glass with a measurement disc are suggested for measuring the blood stains.

Why is it important to select a variety of stains from different areas of the pattern?

Selecting a variety of stains from different areas ensures a more accurate representation of the blood spatter pattern and helps in determining the true area of origin.

What shape should the stains ideally have for easier measurement?

The stains should ideally have an oval shape, indicating an angle of impact of 60 degrees or less.

How does the script suggest documenting the measurements of the stains?

The script suggests documenting the length and width of each stain and then calculating the impact angle using the inverse sine of the width divided by the length.

What is the purpose of finding the point of convergence in the analysis?

The point of convergence helps to pinpoint the area where the blood spatter originated from by intersecting the lines drawn from the center of the stains at their respective angles.

How can the height of the impact be determined using the measurements?

The height of the impact can be determined by using the tangent of the impact angles and measuring the distance from the area of origin to the point where the strings cross.

What alternative method is mentioned in the script for finding the height of the impact?

The script mentions using the tangent of the impact angles to calculate the height for each stain and then averaging those heights for a more accurate measurement.