What Tools Are Used to Collect Bloodstain Evidence?

The tools used to collect bloodstain evidence fall into five working groups: light sources and chemical reagents for finding stains, cameras and scales for documenting them, swabs and cutting instruments for collecting them, paper packaging and refrigeration for preserving them, and personal protective equipment for handling them safely. Each group has its own standards, and a mistake with any one of them can make an otherwise strong sample useless in a laboratory or in court.

Lights and Reagents for Finding Stains

Blood isn’t always visible. Someone may have cleaned a surface, the stain may have soaked into a porous material, or it may have dried against a dark background. Investigators work through two categories of detection tools before anything gets collected.

Alternate Light Sources

Alternate light sources emit specific wavelengths that make biological material easier to see. Untreated blood does not fluoresce; it absorbs UV wavelengths in the 260–400 nm range and shows up as dark patches against the surrounding surface.¹ UV light at 365 nm has proven particularly effective at picking up small traces of blood serum, the clear fluid that separates from clotting blood and often survives a cleanup attempt.²

These lights are a first pass, not a final answer. Background material heavily influences the result, and the absence of a reaction under a forensic light source does not mean no blood is present.³

Chemical Reagents

Luminol is the most widely used chemical reagent. Sprayed on a surface, it reacts with iron compounds derived from hemoglobin and produces a blue-green chemiluminescence visible in a darkened room, often revealing patterns even after someone has scrubbed with cleaning products.⁴ Bluestar operates on the same principle and gives a brighter, longer-lasting glow that does not require full darkness.

Luminol is a presumptive test. Household bleach, copper, steel, horseradish, and even the unfinished edge of drywall can all trigger the same reaction, so a positive result requires confirmatory laboratory testing before anyone can say the substance is human blood.⁵

Cameras and Measuring Tools for Documentation

Before anyone touches a bloodstain, it gets photographed. The documentation becomes the permanent record that investigators, analysts, attorneys, and juries will rely on later.

Photographs are taken in three tiers: overall shots that establish the scene, mid-range shots that fix each stain’s position relative to nearby landmarks, and close-ups that capture detail on individual stains. The scene must first be photographed as-is, before any markers, scales, or other items are added.⁶

Recommended minimum equipment includes a single-lens reflex or mirrorless interchangeable-lens camera, lenses ranging from wide-angle to macro, an external flash unit, a tripod, a remote shutter release, and an off-camera flash sync cord or wireless trigger.⁶ Forensic rulers or scales are placed beside stains when relative size matters, though a scale-free photograph is always taken first. Tape measures and laser rangefinders fix the position of each stain within the broader scene geometry.

Tools for Collecting Wet Blood

Wet blood degrades faster than dried blood and contaminates more easily. The collection tool depends on how much blood is present.

For small deposits, the standard tool is a sterile swab or gauze pad lightly moistened with distilled water, pressed into the stain to concentrate the sample on the tip. Some laboratories recommend following the moistened swab with a second dry swab and submitting both.⁷ Moisture is kept to a minimum so the sample isn’t diluted.

For larger pools, sterile gauze pads absorb more volume than a swab can handle. Pipettes or disposable transfer droppers move liquid blood into sterile tubes when a test requires the sample to stay in liquid form. Every tool that touches a sample must be sterile and used only once; switching to a fresh swab or blade between stains is non-negotiable.

Tools for Collecting Dried Blood

Dried blood is more stable, but recovering it without loss or contamination takes the right tool for the surface it’s on.

Non-Porous Surfaces

When possible, investigators submit the whole item that bears the stain. When that isn’t practical, a clean scalpel or razor blade scrapes the dried flakes onto a piece of clean paper, which is folded into a bindle and placed in a labeled paper envelope. On wood, the stained area is shaved rather than scraped, which recovers more material.⁸

Fingerprint-lifting tape is another option for smooth, non-absorbent surfaces. The tape is pressed over the stain, rubbed firmly with a blunt object, then lifted and placed on a clear acetate backing. Paper backing is not used because it makes later analysis difficult. The lifting can be repeated on the same stain if needed.⁸

Porous Surfaces

Carpet, upholstery, denim, and brick pull blood deep into their fibers or pores, where scraping and swabbing fall short. Cuttings are the simplest answer: a clean blade removes the section of material holding the stain.⁷

When cutting isn’t feasible, forensic wet-vacuum systems offer a more aggressive recovery tool. They spray a buffer solution onto the substrate and simultaneously suction it back up, dislodging embedded cellular material and suspending it in solution. Studies have shown wet-vacuum collection recovers an average of twelve times more DNA than wet swabbing across a range of porous materials.⁹ The tradeoff is cost and time: a unit runs roughly $43,000, and most agencies reserve it for cases where standard methods have already failed on a critical piece of evidence.¹⁰

Substrate Control Swabs

A control swab is taken from an unstained area next to each bloodstain, using a fresh sterile swab moistened with distilled water, then air-dried and packaged in paper.⁸ Laboratories use these controls to check for contamination, troubleshoot PCR inhibition during DNA amplification, and rule out fluorescence interference from the surface material.¹¹ Without them, a defense attorney can argue that a DNA result came from the surface itself rather than from the stain. Skipping this step is one of the fastest ways to create reasonable doubt about otherwise solid evidence.

Packaging and Preservation Supplies

Everything collected at the scene has to survive transport and storage without losing its DNA value. The containers and conditions matter as much as the collection tools.

Paper Containers

Biological evidence goes into paper bags, paper envelopes, or cardboard boxes. Paper is breathable, which lets residual moisture escape. Plastic traps humidity, promotes mold, and can degrade biological material to the point where DNA testing becomes impossible.¹² Every item is air-dried before packaging and stored individually to prevent transfer between samples.

The exception is evidence that is still wet and cannot be dried at the scene. It goes into an impermeable container like a metal can or glass jar, then into refrigeration at 2°C to 8°C (roughly 35°F to 46°F) until it can be dried properly.¹³

Labels and Tamper-Evident Seals

Every package is labeled with the case number, item number, collecting agency, item description, location, date and time, and the collector’s initials. That information establishes the chain of custody, the record of every person who has handled the evidence. If laboratory analysis later shows contamination, this record is the roadmap for finding where it happened.¹⁴ Tamper-evident evidence tape seals each package so unauthorized access shows immediately.

Temperature-Controlled Storage

Long-term preservation comes down to temperature. NIST defines four tiers: frozen storage at or below −10°C (14°F), refrigerated storage between 2°C and 8°C with humidity under 25%, temperature-controlled rooms between 15.5°C and 24°C (60°F to 75°F) with humidity under 60%, and ambient room temperature with no environmental controls.¹³ Liquid samples and items that cannot be dried should be frozen. Properly packaged dried biological evidence stored in a temperature-controlled environment will yield reliable DNA results for decades.¹⁵ Repeated thawing and refreezing degrades DNA and should be avoided.

Personal Protective Equipment

Blood at a crime scene is a biohazard, and federal workplace safety standards require personal protective equipment for anyone with occupational exposure to it.¹⁶ The standard kit for a bloodstain collection includes:

Nitrile or latex disposable gloves, changed between samples to prevent cross-contamination.
Goggles or safety glasses to shield against splashes, especially when spraying chemical reagents.
Masks and face shields for protection against airborne particles or aerosol exposure.
Disposable coveralls, gowns, and shoe covers so biological material isn’t carried away from the scene on the collector’s clothing.

Contaminated materials go into labeled biohazard waste containers for proper disposal. The bloodborne pathogens standard and CDC standard precautions both mandate these protections for anyone who handles blood in a professional capacity.¹⁷

Pattern Analysis Software

The collected evidence often goes beyond identifying whose blood it is; the shape, size, and distribution of stains can reveal the type of force used and the position of a victim. Traditional pattern analysis uses physical stringing, where analysts attach strings to individual stains and trace them back to a common point of origin. Software like HemoSpat now calculates the area of origin digitally, cutting what would be a full day of stringing down to a few hours, and the results can be saved, reanalyzed, and exported into 3D reconstruction software for courtroom use.¹⁸ Newer research has explored iPhone LiDAR sensors and 3D scanning as portable field tools for area-of-origin estimation.

1
Office of Justice Programs. Landscape Study of Alternate Light Sources
2
PubMed. Ultraviolet 365 as an Alternative Light Source for Detection of Blood Serum
3
ScienceDirect. Illuminating the Benefits and Limitations of Forensic Light Sources
4
ScienceDirect. Forensic Application of the Luminol Reaction as a Presumptive Test for Blood
5
National Institute of Justice. Presumptive v. Confirmatory Tests
6
National Institute of Standards and Technology. Standard Guide for Crime Scene Photography
7
National Institute of Justice. Blood and Body Fluid Collection
8
National Institute of Justice. Dry Stains on Non-Absorbent Surfaces
9
ScienceDirect. Pulse Lavage System (PLS) Versus Forensic Wet-Vacuum Collection of Biological Material
10
PubMed. Evaluation of the Microbial Wet-Vacuum System for DNA Sampling
11
National Institute of Justice. Crime Scene and DNA Basics for Forensic Analysts – Collection Techniques
12
National Institute of Justice. Proper Evidence Collection and Packaging
13
National Institute of Standards and Technology. NISTIR 7928 – The Biological Evidence Preservation Handbook
14
National Institute of Justice. Chain of Custody of Evidence
15
National Institute of Standards and Technology. Freezing Biological Evidence – Key Considerations
16
Occupational Safety and Health Administration. 29 CFR 1910.1030 – Bloodborne Pathogens
17
Occupational Safety and Health Administration. Worker Protections Against Occupational Exposure to Infectious Diseases
18
HemoSpat. HemoSpat – Bloodstain Pattern Analysis Software