It started one morning in 1990 with a none-too-promising paint analysis request from a detective working on a burglary at a brand new apartment complex. The burglar had used a levered device to pry open a white painted front door of an apartment that had been occupied for only a few weeks. A suspect was later found loitering in the neighborhood, and he had an outstanding warrant for a prior burglary. A search of the suspect’s vehicle turned up a two-foot long pry bar in the trunk, with some white material transfers on the wedge end.
The analysis request was a criminalist’s trace analysis “ho-hum” case. A single layer of new architectural paint on new wood framing, and a few sub-millimeter scraps of smeared white material on an iron surface. The confirmation of paint similarity between the door frame and pry bar samples was likely to have little uniqueness, and was also likely to lead to a significant amount of reasonable doubt in a typical trial juror’s mind.
After analysis, the detective was called with a “good news, bad news” report. The apartment and pry bar samples were indeed similar and probably rare, but they were rare because they were new paint films and they also contained lead carbonate pigment. Now he had two cases.
Further investigation found that a painting contractor had low-bid the paint job to get rid of an old container of alkyd lead-containing white semi-gloss paint he had “buried” in the back of his warehouse. Save for the burglary, he probably would have gotten away with his dumping plan. Subsequently, the apartment dwellers were moved out, the exterior paint on the building was stripped off and replaced, the painter declared bankruptcy and paid a hefty fine, and the burglar pled out. You and I covered the insurance losses.
Such is the life of a forensic paint examiner/criminalist. Nothing in the case ever got to trial or to the newspapers.
Criminal Forensic Trace AnalysisCriminal Forensic Trace Analysis is one of several fields of Criminalistics that includes Toxicologists, DNA Analysts, Serologists, Drug Chemists and Latent Print Examiners. Trace examinations can involve paint, glass, hair, explosives, fiber, soil, metals and general unknown materials. It is also a field that requires constant study and re-education, due to the daily and weekly introduction of new materials and processing methods into the products a trace criminalist must analyze and compare.
Paint analyses are a particular challenge due to the durability and ubiquity of paint films. A single wall or picket fence in Virginia or Massachusetts might exhibit a hundred years of paint history that can show up as evidence in a murder, hit-and-run or burglary. This is a hint about the profound difference between trace and DNA evidence, where genetic materials have changed little over the eons, and can be expected to change little in the future. Trace evidence changes constantly, and this leads to a constant need for samples of new materials. A criminalist’s success in acquiring new paint materials is at the mercy of the coatings industry.
A significant amount of time is spent in perusing current industrial literature, like PCI, and research journals, and then requesting samples and analyzing new materials. In the case of paint, these materials include resins, pigments, fillers, additives and sample paint panels, as well as MSD sheets and patent information. It’s not unusual to characterize and database analytical results on one or two new products each day. The fundamentals of forensic paint analysis are covered by ASTM Guideline E 1610, in volume 14.02. The characterization normally involves infrared spectrometry (FTIR), electron microscopy-x-ray spectroscopy (SEM-EDS and WDS) elemental analysis, pyrolysis-gas chromatography-mass spectrometry (PGC-MS), color-imetry and refractive index determinations. Dyes are further analyzed by thin layer chromatography (TLC). Some labs include x-ray diffraction (XRD) in their analytical scheme. It’s a time-consuming process, but it’s difficult to identify things we’ve never seen before.
Observation is Key“Opportunistic observation” can be a key phrase in forensic paint examinations. Detectives can’t be expected to request analyses of things they can’t see, so trace examiners need to keep their microscopical eyes open for valuable evidence the detectives might legitimately miss.
Case Example One
A case in point involved another burglary that was possibly associated with a red-handled hatchet, used as a prying device to open a locked window. Once again, the request held little hope of leading to a definitive report and, indeed, the finding of similar red lacquer on the window frame and hatchet handle was hardly a unique piece of evidence. Fortunately, the detective in the case had been thorough, and had collected and submitted as many pieces of damaged framing as he could find. Close examination, under relatively low magnification, showed that a small, half-inch long, damaged fragment of the red paint-smeared frame also exhibited elongated impressions. Examination of a damaged paint area of the hatchet handle showed exposed wood grain that matched the impression in the frame. Suddenly, the detective had definitive evidence to work with, largely due to his thoroughness. The association is shown in the photo.
Case Example Two
At the other extreme in paint examinations is a case that grew out of an accident investigation involving a run in between a passenger car and a tractor-trailer rig. The tractor driver insisted that the car, traveling to his right, cut in front of him and its left-rear fender clipped his right front wheel, causing the car driver to lose control and spin off the highway. The car driver, on the other hand, insisted that the tractor veered right into his car’s left-front fender and caused the accident. The car was old, poorly cared for, and exhibited extensive damage on all quarters. Paint fragments were collected from the tractor’s right front wheel lug-nuts, and the left front and left rear fenders of the car.
Subsequent analysis showed that the front of the car exhibited 14 layers of paint, and the rear, 13 layers. The missing layer at the rear of the car was layer number 8 on the front. A description of all the different paint chemistries encountered is beyond the scope of this short piece, but suffice it to say, the lug-nut samples exhibited 13 layers, and the trucker’s story was found to be true. The car driver was stuck with having to buy and pay for his own, much needed, new car. His existing insurance didn’t cover much.
Case Example Three
Not all criminal trace analyses lead to convictions. They can also lead to the exoneration of suspects or previously convicted persons. A case in point is one where a woman was in a pickup truck with her boyfriend and his brother, going the wrong way on a city freeway. They hit three other cars, and a woman in one of the cars died of her injuries. Two county attorneys at the scene, along with accident investigators, accepted the story of the boy “friend” and his brother that the very intoxicated girl friend was driving. Erroneous, or perhaps presumptive, analyses by blood spatter experts, serologists and accident reconstructionists, supported the men’s stories. The girlfriend was poor, could not post bond and spent nine months in jail waiting for a trial.
A defense investigator later questioned the blood spatter work, and all the physical evidence in the case, (including the truck) was sent to the trace analysis unit for additional work. Once there, a paint/plastic pigmented impact transfer was found on the left knee of the boyfriend’s pants. The transfer coincided physically and chemically with a fabric impression on the left under-side of the dashboard, next to the steering column of the pickup truck.
A few days of work and photography inside the truck, reconstructing the moment of the accident impact and, using lab employees as “dummies”, showed that the girlfriend was the passenger, not the driver. A day later, the girl was released from jail. The boyfriend coincidentally confessed to a cousin, in another state, that he had been the truck driver, but he disappeared and has yet to be found. The case was rewarding from a trace evidence perspective, but the husband of the deceased woman is still unconsoled.
Case Example Four – The Green River Murders
Many other examples of forensic paint analysis abound, and can involve artistic, automotive OEM, repaint, historical, maintenance and architectural finishes – and just about anything else the readers of this magazine have, can or will develop.
A notable example grew out of the Green River Murders case in King County, Washington. Gary Ridgway murdered approximately 50 women during a two- or three-year period in the early 1980s, but had not been charged or tried for those crimes. Many of the victims had been dumped into the Green River outside Seattle. Twenty years later, Skip Palenik, principal of Microtrace LLC in Elgin, IL, was called into the cold case. He was asked to peruse the known victims’ clothing evidence, which had been previously analyzed unsuccessfully, and then held in storage those 20 long years. He and his former assistant, Sarah (Walbridge) Jones, applied micro vacuuming techniques to the clothing, and recovered hundreds of polyurethane paint mist spheres in a wide variety of colors. This writer, and Dr. Brezinski of PCI, were called into the case by the King County prosecutors to assist in evaluating the evidence, analyzing current products and searching for historical paint samples from the early 1980s.
Gary Ridgway, who was an early suspect in the original investigation, had been a custom tractor spray painter in Seattle’s Kenworth painting plant. The prosecution assertion became that Ridgway, who worked in the open-air spray paint shop, collected the mist on his clothing, and transferred it to his victims during his assaults.
The micrometer-sized mist paint particles were analyzed using micro-infrared spectrometry and visible light spectroscopy, and found to be similar to the 2K paint systems Kenworth was using when Ridgway worked for them. Chemists from Dupont were invaluable in supplying known pigment and paint formulations they had produced for Kenworth at the time of the murders. Company data banks of old formulations and even retained paint samples can be of immeasurable historic and forensic value.
Overwhelmed with the paint evidence, Ridgway subsequently confessed before trial and, to avoid the death penalty, led authorities to many murder sites that were previously undiscovered. He apologized for not remembering all of them.
These cases (with a few changes to protect privacy) show some of the challenges and rewards of criminal forensic paint examination. Similar stories of micro-analysis challenges and successes can be told about examinations involving all the other types of materials trace examiners are called to analyze. It’s a rewarding profession. n
For more information, contact Mike at firstname.lastname@example.org.