Sense-making software for crime investigation:

how to combine stories and arguments?

Henry Prakken(& Floris Bex, Susan van den Braak, Herre van Oostendorp, Bart Verheij,

Gerard Vreeswijk)New York,

January 29th, 2007

Contents A research project:

Building software that supports crime investigators

Investigate theoretical basis Stories and causality in evidential reasoning

Abduction Reasoning with testimonies:

Argumentation Combining stories and testimonies:

abduction + argumentation

Practical motivation Crime investigation often one-sided,

aiming to confirm a certain hypothesis

Dutch criminal procedure is inquisitory: Judges rely on police case files Very little investigation in court ...

So a lot can go wrong

The intended software: a sense-making system

No knowledge inside, but Supports human users in structuring and

visualising their thinking Can calculate with these structures Can link them with case files

Should be based on an account of evidentiary reasoning that is:

Prescriptive (supporting rational thinking) Natural (close to the way crime investigators think)

Anchored Narratives Theory

(Crombag, van Koppen & Wagenaar)

A rational and natural theory of evidentiary reasoning?

Recognises importance of stories (timelines!) Generalisations

Find plausible causal links within story Anchor stories in evidence

But theoretically underdeveloped Our aim: investigate theoretical foundations of

ANT Causation Testimonies

Stories involve causation Stories are (at least) a sequence of events

on a timeline Events are supposedly caused by earlier

events Physical causation Mental causation

Reasoning with causal information: Prediction: assume or observe event, predict

what will happen next Explanation: observe event, explain what could

have caused it

Example: the King case (1) Fact: King was beaten up by mr. Zomerdijk

in backyard of Zomerdijk’s house Prosecution’s story

King (a convicted thief) was up to no good King climbs into backyard of Zomerdijk family King enters bedroom King steps on toy Mr. Zomerdijk hears sound Mr. Zomerdijk goes to bedroom King closes door and runs away

Example: the King case (2) Fact: King was beaten up by mr.

Zomerdijk in backyard of Zomerdijk’s house

Defence’s story King climbs into backyard of Zomerdijk family Wind opens bedroom door Wind hits toy Mr. Zomerdijk hears sound Mr. Zomerdijk goes to bedroom Mr. Zomerdijk sees King in backyard

Representing causal knowledge

Explanation with evidential rules:

Deduction:

Explanation with causal rules:

Abduction:

Effect CauseEffect Cause

Cause EffectEffect Cause

Fire causes Smoke

Smoke

Fire

Smoke means Fire

Smoke

Fire

Abductive-logical models

Simulate abduction with deduction: Given:

causal rules T ‘explanandum’ F

Hypothesise a cause C such that T with C logically implies F (“C explains F”)

Compare all alternative explanations How much additional evidence is explained? How much additional evidence is contradicted? …

Explanations as causal networks of events

Toy makes a sound

ObservationsThe door is closed

Explanations as causal networks of events

Toy makes a sound

ObservationsThe door is closed

King enters house

King stepson toy

King closesdoor

Explanations as causal networks of events

Toy makes a sound

ObservationsThe door is closed

King enters house

King stepson toy

King closesdoor

The wind hits the toy

The wind closes

the door

The wind opens

the door

Loud bang

Explanations as causal networks of events

Toy makes a sound

ObservationsThe door is closed

King enters house

King stepson toy

King closesdoor

No loud bangwas heard

The wind hits the toy

The wind closes

the door

The wind opens

the door

Loud bang

A problem(?): testimonies must also be explained

King enters house

King stepson toy

Toy makes a sound

Observations

The door is closed

King closesdoor

Witness wants toprotect himself

Witness Z often imagines sounds

Witness Z says“I heard a sound”

Witness Z says“the door was closed”

Testimony principle is not a causal but an evidential

rule Testimony principle not represented from-

cause-to-effect:

but from-cause-to-effect:

Truth of P is the usual cause of “P”. Other causes of are exceptions.

Reasoning is then modelled as constructing and comparing (defeasible) arguments

Witness says “P” => P

P => Witness says “P”

Combining abduction and argumentation

Toy makes a sound

‘Observations’The door is closed

King enters house

King stepson toy

King closesdoor

Witness Z says“I heard a sound”

Witness Z is not sincere

Witness wants toprotect himself

Further evidence needed!

The full picture

Toy makes a sound

ObservationsThe door is closed

King enters house

King stepson toy

King closesdoor

No loud bangwas heard

The wind hits the toy

The wind closes

the door

The wind opens

the door

Loud bang

Conclusion Combining abduction for representing

stories and argumentation for reasoning about sources of evidence arguably is natural can arguably be given a sound rational

basis But all this should be further

investigated

Arguments

Assault

e1 e3

e2

hitting

p

intent

Counterarguments

Assault

e1 e3

e2

hitting

p

intent

Selfdefence

attacked

e4

e5q

Reinstatement

Assault

e1 e3

e2

hitting

p

intent

Selfdefence

attacked

e4

e5q

Not attacked

e6 e7