Are there

smaller circular 

stains

surrounding a 

larger stain 

AND present on

a horizontal 

surface?

Is there 

linear or 

curvilinear 

distribution?

Are there 

smaller 

stains that 

converge 

to a larger 

stain?

Is there a 

progressive 

change

in 

shape?

(W/L 

ratio)

N

Y

N

Is there a large

stain on a 

horizontal 

surface?

N

Is there an area 

of 

convergence?

N

Conclude:

Spatter 

Consider: Forward 

spatter, 

Backspatter OR 

Cessation

Conclude:

Impact

Consider: Forward 

Spatter

Backspatter OR

Cessation

Y

Are line 

structures

present?

(possible 

mucous)

Y Y

Conclude:

Expiration

Are there one or 

more stains 

with

a lighter color

(possible 

saliva) or stains 

with vacuoles?

N

Conclude:

Expiration

Y

Conclude:

Projected or 

Expiration

N

Is there color

intensity 

variation 

not

attributable

to gravity

in the 

larger

stain?

Y Y

Conclude:

Projected

Splash

N

Conclude:

Impact pattern with a 

transfer stain at 

the convergence

Consider:

Altered

Splash OR

Projected

Y

Conclude:

Projected

N

Conclude:

Cast-off

Y

Are there 

large

spiny edge 

character

istics?

Conclude:

Drip Pattern

N

Conclude:

Splash

Y

Presume

blood

stain

Is the target

porous?

Stop

Y

Is the stain

circular 

or

elliptical?

N

Y

Are there 

asymmetric 

variations

in color intensity 

not attributable

to gravity OR 

texture not 

accounted

for by target 

surface?

Conclude:

Transfer

Y

Is there 

more 

than

one 

stain?

N

Are all stains 

greater

than 4mm 

with 

downward 

directionality

?

Y

Is there a 

distribution

of 3 or 

more of 

these 

stains

between 

two

points?

Conclude:

Drip stains

Conclude:

Drip trail

Consider 

Cast-off

Y

N

Is there a 

stream

with edges 

that are

nearly parallel 

and

linear or 

curvilinear?

N

N

Y

Conclude:

Transfer

Is there an

accumula

tion of 

blood

in excess 

of 20mm

in width?

Conclude:

Pool

N

Y

Are 

perimeter 

stains

present?

Conclude:

Wipe

Y

Are 

(smudged 

or

feathered) 

features

present?

N

Conclude:

Swipe 

OR 

Wipe

Y

Are 

striations

present 

in stain?

N

Y

Conclude:

Transfer

Conclude:

Swipe 

OR

Wipe

N

Y

Is the 

stain 

greater

than 4 

mm in 

width?

Is the stain 

larger 

than

20 mm?

Conclude:

Spatter

Conclude:

Pool

Y Y

Does the 

shape of

the stain 

indicate

downward 

directionality?

N N

Conclude:

Drip 

Consider

Spatter

Conclude:

Spatter

Y

N

N

N

N

B1

A1

A2

B2

C1

A4

B3 B4

B5

C2

A5

A6

A7

C4 C3

D1

D4 D3

D6 D5

D7

D8

Bloodstain Pattern Classification Process Map 

Version 2.3

18 December 2019

NIST OSAC BPA Subcommittee

Are there 

asymmetric 

variations

in color intensity 

not attributable

to gravity OR 

texture not

accounted for 

by target surface?

N

Conclude:

Flow

Y

A3

D2

Read Me

This Bloodstain Pattern Classification Process Map attempts to provide the correct classification of bloodstain patterns based upon observed physical features. Each 

decision is based upon these observed physical features, not the mechanisms by which the pattern or stain was created.

This process map is intended for use by bloodstain pattern analysts trained to competency. 

A stain is defined as a single contiguous area containing blood. 

This process map may be utilized to: identify research needs, improve methods, articulate and visualize the classification process, provide a basis for proper documentation, 

articulate how observations lead to classifications, support training, understand cumulative error, and design a quality program to address said errors.

Bloodstain pattern classification does not conclude at the yellow parallelograms. Analysis may continue by taking into account information that may further 

inform the classification.

A0