View Full Version : D20 forensics (rules for 3.5E and D20 Modern)

2008-07-20, 07:34 AM
I got this idea while I was working on my Monster Contest entry (the idea for chromatography using checks popped into my head). Basically these are just rules for checks used to find evidence in a CSI like manner. All checks are made using an existing skill (unless the character has the Forensic Investigator feat, see below). Synergy bonuses apply to Forensics checks as if they were the type of check which is used as a modifier.

The roll for a forensics check is calculated thus: 1d20 + (Int Modifier) + (Ranks in appropriate skill) + (Bonuses and penalties).

The DC for a forensic check is: Base DC + (DC modifiers) + (Circumstance Modifiers)

The following table lists Circumstance Modifiers (which increase or reduce the DC). DC modifiers are Circumstance modifiers which only apply to specific types of check and are listed elsewhere. Regardless of modifiers the DC of a check can never be lowered below 5.

{TABLE=head]Circumstance|DC Modifier

Samples are tested the moment they were found|-10
Samples were gathered and sealed in a clean container|-5
Samples were contaminated|+10
Samples are tested in a specifically prepared lab area (500gp/Purchase DC 15)|-10
Evidence was gathered within 12 hours of the event|-5
Evidence was gathered over 48 hours after the event|+5, and plus another 5 per month
Evidence was exposed to the elements or attempts were made to clean it away|+5[/TABLE]

When a check is made then the DC should be subtract from the roll. If the result is positive then the check succeeds, if it is negative it fails. After this, roll a percentile dice and compare the results to the success or failure table as appropriate. If the failure table comes up "False Positive" then the player rolls again, from the success table, but the information they gain is inaccurate.

Forensics Checks

The checks are outlined using the format in the spoiler tags below;

Name (System)


Base DC:
Success Table:
Failure Table:

System: if the check can be made in 3.5E, d20 modern or both.
Results: What information the test is supposed to find
Base DC: The DC of the skill check before modifiers are added.
Skill: The skill necessary for the check.
Modifiers: The DC modifiers exclusive to a check
Procedure: What must be done to carry out the check (mostly for flavour)
Tools/Equipment: What is needed to carry out the check
Time: How long the check takes to carry out
Cost: The overall cost of paying an NPC to do the test (including the cost of consumable equipment and tools and payment of whoever carries out the test)
Success Table: The table to compare the results of the percentile roll to determine the information gained
Failure: The table to establish the effects of a failed test.

Chemical Comparison (Both)

Compares one sample of a chemical to another. Finds whether or not the second sample contains or is the same as the first.

Base DC: 5
Skill: Craft (Alchemy)/Craft (Chemical) or Craft (Pharmaceutical)
Modifiers: Impure comparison sample (+5)
Procedure: The samples are placed on separate dimpled trays (one sample in each dimple) and a series of different tests are applied to each of these samples. The two trays are then compared.
Tools/Equipment: 2 clean dimpled trays (2sp/DC 1), testing chemicals (3g/DC 5 for 50 tests worth)
Time: 1 hour
Cost: 5gp/DC 5
Success Table:
{TABLE=head]% Roll|Result

1-25|Presence or lack thereof

26-75|Quantity of substance present

76-100|Other substances present in the sample[/TABLE]
Failure Table:
{TABLE=head]% Roll|Result

1-75|Inconclusive results

76-100|False positive[/TABLE]

Magic Level Check (3.5E)

Tests a substance or item for the presence of magic (as a detect magic spell can be used)

Base DC: 5
Skill: Use Magical Device
Modifiers: n/a
Procedure: A magical device known as a thaumometer (Craft wondrous item, detect magic, 100 XP, 10 gp) is used. This consists of a strip of metal (resembling a steel ruler) which is placed on whatever is being tested. A mark appears and indicates the level of magic present near the device (although the user must account for nearby magic which may be detected by the device and skew the results).
Tools/Equipment: A thaumometer (15 GP)
Time: 1 standard action
Cost: 50sp
Success Table:
{TABLE=head]% Roll|Result

1-25|Presence or lack thereof of magic

26-75|Confounding sources of magic (i.e. anything else that the thaumometer might be detecting)

76-100|The level of magic present in the specimen[/TABLE]
Failure Table:
{TABLE=head]% Roll|Result

1-75|Inconclusive results

76-99|False positive

100|User breaks the thaumometer[/TABLE]

Study Biomatter (Both)

Either a DNA test (d20 modern) or a magical version thereof.

Base DC: 10
Skill: Use Magical Device/Craft (Electronic)
Modifiers: Unclean machine (+10)
Procedure: A magical device or DNA testing machine is used to analyse a sample of living matter from a creature. The result can be used in a compare reading test or analyse biomatter test (see below)
Tools/Equipment: Essence Detector/Centrifuge (1000gp/DC15), Lab equipment (50gp/DC5)
Time: 48 hours
Cost: 100gp/DC7
Success Table: n/a, success always gives an accurate readout
Failure Table:
{TABLE=head]% Roll|Result

1-99|Test sample is ruined

100|Machine is damaged[/TABLE]

Lift Fingerprint (both)

Collects and stores a fingerprint left on a surface. Can also be used to gather and store the fingerprints of a single willing target.

Base DC: 5
Skill: Search/Investigate
Modifiers: Rough or porous surface (+5), smooth surface (-5)
Procedure: Fine powder is spread over a surface. It is then brushed away. The powder sticks to and reveals any fingerprints left behind. The print can then be recorded by "lifting" it with tape or specially prepared parchment.
Tools/Equipment: Fingerprint powder (3gp/DC3 for enough to ), fine brush (2gp/DC2), fingerprint board (50sp/DC1)
Time: 1 full round action per square foot searched
Cost: 5gp/DC3
Success Table:
{TABLE=head]% Roll|Result

1-90|Fingerprint is lifted

91-100|Clear fingerprint, +1 bonus to any checks using the print.[/TABLE]
Failure Table:
{TABLE=head]% Roll|Result

1-75|Print is not revealed

76-99|Print is ruined and cannot be recovered

100|User ends up gathering their own prints[/TABLE]

Compare Readouts (Both)

Compares two readings from either a biomatter test or raise fingerprint check to see if they come from the same creature.

Base DC: 10 (concentration check)/5 (computer use)
Skill: Concentration/Concentration OR Computer use
Modifiers: n/a
Procedure: The two readings or fingerprints are compared to see if they match. A computer may be used for this in d20 modern.
Tools/Equipment: A computer database and scanner (DC15)
Time: 1 full round action per check. Computer analysis takes a full round action plus 3d10 minutes to search its database.
Cost: 5gp
Success Table: n/a Confirms presence of fingerprint or not
Failure Table:
{TABLE=head]% Roll|Result

1-75|Inconclusive results

76-99|False positive

100|User crashes the computer or loses one of the prints[/TABLE]

Analyze Biomatter (Both)

Tries to gather information about a creature based on a Study Biomatter Check

Base DC: 15
Skill: Heal
Modifiers: n/a
Procedure: The reading from a Study Biomatter check is analysed for infomation.
Tools/Equipment: none
Time: 1d12 x 30 minutes
Cost: 50gp/DC7
Success Table:
{TABLE=head]% Roll|Result

1-25|Creature the biomatter originated from

26-75|Above plus specific characteristics (e.g. gender, appearance)

76-100|Above plus allergies, genetic illnesses and other unusual characteristics[/TABLE]
Failure Table:
{TABLE=head]% Roll|Result

1-75|Inconclusive results

76-99|False positive

100|User loses the reading[/TABLE]

Autopsy (Both)

Studies a corpse to find out about how it died.

Base DC: 15
Skill: Heal
Modifiers: n/a
Procedure: The skin is checked for bruises. The corpse is sliced open and the organs examined for damage. The blood is checked for poisons.
Tools/Equipment: Scalpel (5gp/DC3), Poison Test Kit (2gp/DC2)
Time: 1-5 hours
Cost: 100gp/DC10
Success Table:
{TABLE=head]% Roll|Result

1-25|Details of creature (e.g. race, age, etc)

26-75|Above plus cause of death (e.g. weapon injury, illness, old age)

76-100|Above plus specific cause of death (e.g. weapon used, age at time of death)[/TABLE]
Failure Table:
{TABLE=head]% Roll|Result

1-75|No information gained

76-99|Corpse is damaged and evidence lost

100|Corpse comes back as undead (3.5e and appropriate d20 settings only)[/TABLE]

Forensic Investigator [General]
You are an expert in studying evidence.
Prerequisites: Investigator feat, a total of at least 15 ranks in the skills search, concentration, craft (alchemy/pharmaceutical) and heal
Benefits: When you make forensic checks you may use your ranks in forensics. Your ranks in forensics is considered equal to the total of your ranks in search, concentration, craft (alchemy/pharmaceutical) and heal, to the maximum ranks allowed by your class level.
Normal: You must use your ranks in the relevant skill as a modifier when making forensics checks

Pie Guy
2008-07-20, 09:47 AM
I love th e failure for autopsy. (Crap, i cut off the victims head with my scalpel. Wait, it just moved! "Run for your life! Headless zombie!")

2008-07-21, 04:47 AM
Has anyone got any other thoughs?

2008-07-21, 10:35 AM
Thaumometer? Like, Discworld thaums?

I think I'd up the DC for most, if not all, of the checks by 5 or 10.