Police Investigation Quick Start Guide

Purpose: Rapid reference for professional police investigation frameworks Time to read: 5 minutes Full document: 01-police-investigations.md

60-Second Overview

5WH Framework: What, Who, When, Where, Why, How - structures every investigation
PEACE Model: Evidence-based interview technique (Planning, Engage, Account, Closure, Evaluation)
CPIA Duty: Pursue reasonable lines of enquiry both TOWARDS and AWAY FROM suspect
Chain of Custody: 5-step FBI protocol ensures evidence admissibility
PIP Levels: 4-tier competency structure (Volume → Serious → Major → Strategic)

Key Framework: 5WH Investigation Model

┌─────────────────────────────────────────────────────────────┐
│                    INVESTIGATION CORE                       │
├──────────┬──────────┬──────────┬──────────┬──────────┬─────┤
│   WHAT   │   WHO    │   WHEN   │  WHERE   │   WHY    │ HOW │
│ happened?│ involved?│occurred? │took place│ happened?│ done│
├──────────┼──────────┼──────────┼──────────┼──────────┼─────┤
│ Event    │ Victims  │ Timeline │ Crime    │Motivation│Modus│
│ Offence  │ Suspects │ Sequence │ scene    │ Context  │Tools│
│ Classification│Witnesses│ Dating │2ndary loc│Factors │Method│
└──────────┴──────────┴──────────┴──────────┴──────────┴─────┘

Application: Every investigative action must advance understanding of ≥1 dimension

Essential Tools

Tool	Purpose	Link/Reference
PEACE Interview	Evidence-based interviewing	College of Policing APP
HOLMES2	Major incident case management	Police ICT Company
MG Forms	Prosecution file structure	CPS guidance
CPIA Codes	Disclosure obligations	Legislation.gov.uk
ABE Guidance	Vulnerable witness interviews	Ministry of Justice

PEACE Interview Workflow Checklist

P - Planning and Preparation

Review all available evidence
Identify information gaps and objectives
Prepare open-ended questions (not leading)
Consider vulnerability/special measures
Arrange appropriate environment

E - Engage and Explain

Establish rapport (essential for recall)
Explain process and legal rights
Create psychologically safe environment
Clarify expectations

A - Account, Clarify, Challenge

Obtain free narrative (uninterrupted)
Clarify ambiguities using open questions
Challenge inconsistencies with evidence
Allow explanation of discrepancies

C - Closure

Summarize key points
Allow additions/clarifications
Explain next steps
Thank interviewee

E - Evaluation

Evidence base: PEACE produces more reliable evidence than confrontational methods, reduces false confessions

Chain of Custody 5-Step Protocol

Critical: Broken chain = evidence inadmissibility = case collapse

Step 1: Obtain Evidence Legally

Search warrant or legal authority documented
Consent properly recorded
Legal basis clear

Step 2: Describe in Detail

Physical description (size, color, condition)
Location where found (precise)
Date, time, environmental conditions
Photographic documentation

Step 3: Identify Accurately

Unique identifiers/serial numbers
Exhibit numbering system
Label: case number + date + collector initials

Step 4: Package Properly

Evidence-specific packaging (paper for biological, anti-static for digital)
Tamper-evident sealing
Contamination prevention
Preservation (refrigeration/secure storage)

Step 5: Establish Chain of Custody

Chronological possession documentation
Transfer logs with signatures
Storage location logs
Access records
Analysis documentation

Documentation must include: Date/time, collecting officer, receiving officer, purpose, location, condition

CPIA Disclosure Requirements (Plain Language)

Core Duty

Disclose all material that:

Undermines prosecution case, OR
Assists defence case

Not limited to admissible evidence

Reasonable Lines of Enquiry

Pursue enquiries TOWARDS suspect (inculpatory)
Pursue enquiries AWAY FROM suspect (exculpatory)
Document rationale for not pursuing lines

Unused Material

Record ALL material obtained
Retain until case closed + appeals exhausted
Prosecutor reviews and schedules
Sanctions for non-disclosure: case dismissal, conviction overturn

Key Principle

Professional investigation ≠ advocacy. You must gather evidence that both supports AND contradicts working hypothesis.

Critical Standards (Must-Follow)

PACE 1984 (Police and Criminal Evidence Act)

Arrest: Necessity test, reasonable grounds, caution
Detention: Custody officer independence, reviews every 6/9 hours, max 24 hours (36 for indictable)
Interviews: Audio/video recording mandatory, legal advice right, appropriate adult for vulnerable
Search: Warrant required for premises (exceptions documented)

Professional Investigation

Primacy of Material: All conclusions supported by evidence
Objective Evaluation: Systematic consideration of alternatives
Documentation: Contemporaneous recording of all actions/decisions
No Speculation: Assumptions explicitly identified and tested

Digital Evidence

Forensic imaging (bit-by-bit copy)
Hash certification (SHA-256)
Write-blocking during acquisition
Metadata preservation
Analysis on copy, not original

Common Pitfalls (Top 5)

Mistake	Impact	Mitigation
Confirmation bias	Miss exculpatory evidence	ACH methodology, test counter-hypotheses
Broken chain of custody	Evidence inadmissible	Document every transfer, sealed packaging
Leading questions	Unreliable accounts	PEACE training, open questions only
Disclosure failures	Case collapse, sanctions	CPIA compliance, unused material schedules
Inadequate documentation	Accountability gaps	Contemporaneous notes, decision rationale

Specific Warning: Reid Technique

DO NOT USE: Linked to false confessions (25% of DNA exonerations), scientifically discredited behavioral analysis, not evidence-based. Use PEACE instead.

Quality Gates (When to Pause)

Before Arrest

Sufficient evidence for reasonable suspicion?
Necessity test met? (Can investigation proceed without arrest?)
Legal authority confirmed?

Before Interview

All available evidence reviewed?
Vulnerability assessment conducted?
Legal advice offered/declined?
Recording equipment tested?

Before Charging

Evidence meets Code for Crown Prosecutors test?
Exculpatory evidence considered?
CPS consulted for complex cases?
Disclosure obligations understood?

Before Court

Prosecution file complete (MG forms)?
Disclosure schedule prepared?
Witnesses available and briefed?
Evidence admissibility confirmed?

Integration with Phronesis FCIP

Evidence Collection

5WH tagging: Tag documents with relevant dimensions (Who, When, Where, etc.)
Chain of custody: Automated hash generation, transfer logs, access audit trails
Metadata preservation: Capture and protect file metadata

Analysis

Timeline construction: Map events to 5WH framework
Contradiction detection: Flag inconsistencies across witness accounts
Evidence linking: Associate findings with source documents (Bates-style referencing)

Quality Control

CPIA compliance: Track both inculpatory and exculpatory evidence
Disclosure schedules: Auto-generate unused material lists
Audit trails: Complete documentation for accountability

Reporting

MG form templates: Structure exports to prosecution standards
Objective language: Facts-only reporting, conclusions separated
Evidence provenance: Every finding cites supporting material

PIP Competency Levels

Level	Role	Responsibility	Complexity
PIP 1	Volume Crime Investigator	Burglary, theft, initial response	Routine
PIP 2	Serious Crime Investigator	Assault, rape, robbery	Complex
PIP 3	Senior Investigating Officer (SIO)	Homicide, terrorism, organized crime	Major
PIP 4	Strategic Manager	Multiple investigations, policy	Strategic

Requirement: Investigators must be PIP-qualified for case complexity. SIO (PIP 3) required for major incidents.

Quick Reference: Interview Types

Method	Purpose	When Used	Key Techniques
PEACE	General interviewing	All cases	Free narrative, open questions
Cognitive Interview	Enhanced witness recall	Cooperative witnesses	Context reinstatement, report everything, different perspectives
ABE	Vulnerable witnesses	Children, learning difficulties	Video recording, rapport-building, communication aids

Performance: Cognitive Interview increases recall 46% (90% accuracy maintained)

IOPC Standards (External Oversight)

When IOPC Involved

Deaths in custody/following police contact
Serious use of force
Serious sexual offences by officers
Serious corruption
Discriminatory behavior

Investigation Requirements

Independence (no force involvement for serious cases)
Evidence-based decision-making
Organizational/systemic factors considered
Trauma-informed approach
Regular family updates

Key Insight

Individual accountability + organizational accountability. Many serious incidents result from systemic failures, not merely individual error.

Resources and Standards

Primary Sources

College of Policing: Core Investigative Doctrine, PIP guidance
PACE Codes of Practice: Codes A-H (stop/search through terrorism detention)
CPIA 1996: Disclosure obligations and reasonable enquiry
IOPC Statutory Guidance: Investigation standards and learning

Key Cases

Zubulake v. UBS Warburg (2004): Duty to preserve evidence when litigation reasonably anticipated
Da Silva Moore v. Publicis (2012): Technology-assisted review approval

Training

National Detective Programme
PIP Level 1-4 courses
Cognitive Interview training (Fisher & Geiselman methodology)

Cognitive Interview Prompt Questions

Context Reinstatement

"Take me back to that moment. What did you see around you?"
"What sounds do you remember?"
"How were you feeling at the time?"

Report Everything

"Tell me everything, even if it seems unimportant."
"Include any impressions or partial information."
"Don't filter - just describe what you recall."

Different Perspectives

"What might [other person present] have seen?"
"If I was standing where you were, what would I have observed?"

Different Orders

"Start with what you remember most clearly."
"Now tell me what happened just before that."
"Work backwards from the end."

Caution: Clearly distinguish observed facts from inferences

Document Control

Version: Quick Start 1.0 Date: 2026-01-17 Source: 01-police-investigations.md (43,470 bytes) Lines: ~490 Format: Reference card (printable)

Next steps: Read full methodology for:

HOLMES2 system architecture
Major Incident Room coordination
Statement reader protocols
Digital forensics standards (NIST)
International standards (INTERPOL, IACP)

"Investigation is fundamentally human. Systems must support investigative thinking, not replace it. Structure enables accountability while preserving the analytical judgment essential to effective investigation."