Grid Search Method: Procedure, When to Use With Examples

The grid search pattern method is an efficient and thorough crime scene search technique that involves conducting a double-line search— first in one direction, and then in a perpendicular direction.

Other Names: Modified line or double line method.

It aims to maximize evidence detection and minimize the risk of overlooking crucial clues, although it can be time-consuming.

The method employs multiple searchers who systematically cover the area in both directions, enhancing the accuracy and thoroughness of the search process. 

When to Use Grid Search Pattern Method?

• Large outdoor or indoor crime scenes.
• Crime scenes with potential for small or easily overlooked evidence.
• Scenes with a significant amount of evidence scattered throughout the area.
• Small or easily overlooked evidence such as looking for minute traces of blood or fibers at a crime scene.
• Multiple incidents or cases involving several suspects
• When other crime scene search methods, such as line or strip searches, are considered less effective.

Procedure for Grid Search Pattern Technique

Follow the steps to conduct a grid search:

1. Define Search Area: Identity the boundaries of the crime scene or area to be searched. 

2. Divide the Area into Smaller Grids: Break the area into smaller, manageable grids, considering the size of the area and the type of evidence being sought.

3. Mark the Grids: Physically mark the grid lines using string, tape, or other markers to create clear search lanes.

4. Assign Searchers: Allocate searchers to each grid or lane, ensuring they are aware of their assigned search direction.

5. Conduct the First Pass of the Search: Searchers move through their assigned lanes in one direction, closely examining the area for evidence.

6. Realign the Grids to 90°: Once the first pass is complete, reposition the grid markers at a 90° angle to the original search direction.

7. Conduct the Second Pass of the Search: Searchers move through their reassigned lanes in the new direction, effectively covering the same area a second time.

8. Collect and Document Evidence: As evidence is found, searchers must collect, document, and preserve it according to proper procedures.

9. Conclude the Search: Once the entire area has been thoroughly searched in both directions, conclude the search, and proceed with further crime scene investigation tasks.

How to do Grid Pattern Searches at Crime Scenes? (Practical Examples)

Case History: A small passenger bus has crashed in a remote forested grass field area, leaving debris scattered across a wide zone. 

Goal: Search to locate and collect relevant evidence.

Investigator’s Opinion on Choosing Search pattern: Due to the size and complexity of the scene, a grid search method is employed to ensure a systematic and comprehensive examination of the area.

Step 1: Establish the Search Area

• Determine the boundaries of the search area based on the plane’s flight path, debris distribution, and environmental factors.
• Mark the perimeter of the search area using flags or other visible markers.

Step 2: Divide the Area into Grids

• Using measuring tapes or similar tools, divide the search area into equal-sized grids. Assign a unique identifier to each grid for documentation purposes.
• Ensure each grid is small enough for thorough searching, taking into account the terrain and vegetation.

Step 3: Assign Search Teams

• Divide searchers into teams, with each team responsible for a specific grid.
• Equip each team with necessary tools, such as metal detectors, evidence bags, and cameras.

Step 4: Conduct the First Pass of the Search

• Teams systematically search their assigned grids, moving in one direction (e.g., north to south).
• Searchers carefully inspect the ground, vegetation, and any debris for evidence, documenting and collecting findings as necessary.

Step 5: Realign Grids for the Second Pass

• Once all teams have completed the first pass, remove the initial grid markers and reposition them at a 90° angle to the first search direction (e.g., east to west).
• Reassign teams to the new grids, ensuring that a different set of searchers covers each area for the second pass.

Step 6: Conduct the Second Pass of the Search

• Teams repeat the search process in the new direction, further ensuring the thoroughness of the investigation.
• Document and collect any additional evidence discovered during the second pass.

Step 7: Compile and Analyze Collected Evidence

• After completing both passes, gather all documented evidence and compare findings between the two search passes.
• Analyze collected evidence to help reconstruct the events leading to the crash and assist in the subsequent investigation.

Advantages

• Ensures that no areas are left unsearched because of thorough search using smaller grids.
• Ensures that two different searchers examine the same area, increasing the chances of finding all relevant evidence.
• Can be adapted to various environments, including large outdoor scenes and indoor locations.
• Allows for better organization and coordination among investigators during the search process.

Disadvantages

• More time-consuming than some other search methods due to the need to search the area twice.
• Requires precise marking and repositioning of search lanes, which can be challenging in some environments.
• The process of marking the grid lines and moving through the area multiple times may inadvertently disturb or contaminate evidence. 

Precautions

• Properly plan and divided the area into manageable grids.
• Equip searchers with appropriate safety gear, such as gloves, boots, and protective clothing.
• Brief searchers on how to handle and preserve evidence.
• Maintain accurate records.
• Train searchers in evidence collection.
• Establish clear communication between search teams and coordinators.

Challenges in Grid Crime Scene Pattern Search Method

• Difficult terrain and environmental factors.
• Large search areas can be time-consuming and resource incentive.
• Uneven ground, dense vegetation, or other natural obstacles makes the grid search method more challenging.
• Heavy rain, snow, etc can hinder the effectiveness of the search process.
• Limited personnel or equipment availability.
• Double-pass nature of the grid method can strain available resources.

General FAQs

References:

• Crime Scene Management within Forensic science [link]
• UAV‐assisted real‐time evidence detection in outdoor crime scene investigations [DOI]
• Henry Lee’s Crime Scene Handbook By Henry C. Lee, Timothy Palmbach, Marilyn T. Miller [link]
• Spiral (Circle) Search Patterns: Procedure, When to Use With Examples [link]