How Reality Capture Helped Map the Truth in a Stray-Bullet Shooting
On June 16, 2013, 23-year-old Alyssa Christine Smith was celebrating Father’s Day with her family at a barbecue in the backyard of her parent’s home in rural Ferndale, Washington. She was picking flowers with the younger children when bullets from what sounded like automatic gunfire suddenly began crackling through the branches of the tall cedar trees overhead. Although family members searched for the shooters and yelled for them to stop, the gunfire continued. Before the family could get to safety, Alyssa was struck and killed by one of the bullets.
Whatcom County Sheriff’s deputies quickly traced the source of the gunfire to a group of shooters who had been taking target practice about 800 yards away on the east bank of the Nooksack River. What they didn’t know was who had pulled the trigger on the gun that killed Alyssa and how the bullet had traveled its fateful path.
Detectives from the Whatcom County Sheriff’s Office requested the assistance of Washington State Patrol’s (WSP) Crime Laboratory, who found themselves faced with one of the largest and most challenging crime scene reconstructions they had ever encountered. “Was a direct shot possible given the scene topography? That was the one question we needed to answer,” said Rick Wyant, forensic firearms unit supervisor for the WSP’s Crime Laboratory. “We needed data that would map the scene for us accurately.”
For help in solving this complex forensic mapping challenge, the WSP turned to the Leica Geosystems Public Safety Group (PSG).
Identifying the Right Mapping Tools
A longtime user of the Leica ScanStation 3D laser scanning technology, WSP’s Crime Laboratory had already worked closely with the Leica Geosystems team to clear up other mapping-related challenges. Integrating the Leica ScanStation into the WSP’s accredited Crime Scene Response Team (CSRT) had provided invaluable insight into numerous death investigations, including officer-involved shootings and other felony crimes. However, the type of shooting that had occurred in Ferndale was unusual, and the size of the crime scene eclipsed anything the WSP had dealt with previously. The 800-yard-long scene encompassed the Nooksack River and a long expanse of open ground with varying elevations that terminate in the forested backyard of the Smith property.
To supplement the data from the WSP’s Leica ScanStation, the Leica Geosystems PSG team recommended capturing high resolution aerial images and videos with the Leica Aibot unmanned aircraft system (UAS, also called a UAV or drone), and coordinating all of the photo control targets and traverse points with a Leica Global Navigation Satellite System (GNSS) rover. The SmartNet RTK network would provide robust, traceable and repeatable corrections at centimeter-level accuracies tied to a common datum, which was essential for the investigation.
On September 9, 2014, a Whatcom County Superior Court judge signed a search warrant for all of the properties comprising the crime scene, allowing for the “collection of 3D aerial and ground scanning, scan data, photographs, video, documentation and placement of instrumentation for measurements for analysis and reconstruction.” With the warrant in hand, the team comprising Leica Geosystems PSG staff, WSP forensic scientists, and Whatcom County detectives was ready to begin collecting data
Airborne Mapping with a UAV
September 16, 2014, broke warm, clear and calm along the Nooksack River in Ferndale—ideal conditions for airborne mapping. A location in an open field about halfway along the alignment axis was chosen as the staging area for vehicles and equipment. While the Leica Geosystems team put the Aibot through a series of pre-flight safety checks, others provided direction to the WSP scan team on where and how terrestrial laser scanning was to take place.
Just prior to the first flight, 4-inch white targets (bathroom tiles) were placed on either side of the alignment by pacing and “wing-dinging,” a not-so-sophisticated surveyor’s method of estimating when one is 90 degrees off and along an alignment. This method turned out to be entirely suited for the task at hand, as the subsequent least squares bundle adjustment proved out.
The flight mission was divided into four separate flights to cover the field and river section, the field near the tree line at the Smith property, and the Smith property itself. Each flight took about seven minutes to execute. The UAV collected images from an elevation about 200 feet above the terrain. The fourth and final flight was launched from small half-size basketball court on the Smith property surrounded by tall trees, and the vertical ascension capability of the Aibot was critical for this task. Unlike a fixed-wing UAV which requires a substantial runway for takeoff-and-landing, the Aibot can take off straight up, automatically fly a pre-programmed mission before returning, and safely land with a vertical descent. The aircraft has a ground detection sensor that stops it about five feet above the ground so the pilot can take control to ensure a smooth landing.
Laser Scanning in Traverse Mode
While the Leica Geosystems UAV team was flying missions, the WSP CSRT was deploying their ScanStation in traverse mode in the Smith’s backyard and later down by the river. Operating in traverse mode was a key workflow for this investigation since parts of the Smith backyard are covered with tall trees that the UAV could not penetrate to “see” through to the ground. For this process, a classic surveyor’s open-ended traverse using assumed coordinates was established using 60 penny nails driven into the ground. Some of these monuments were visible from the sky, enabling GPS/GNSS positioning by the Leica GS14 GNSS receiver later on. A second open-ended traverse was established along the riverbank where a detailed understanding of the terrain was desired. The WSP scanned from a total of eight traverse points.
Using GNSS to Achieve a Common Datum
The UAV and laser scanning data collection took about half a day and went as planned, yielding a large mass of data that needed to be unified into a common 3D coordinate system for analysis. To facilitate the unification process, a member of the Leica Geosystems PSG team walked the length and breadth of the project using the Leica GS14 rover (with RTK corrections provided by SmartNet) to coordinate the photo control targets and traverse points. These centimeter-level 3D coordinates provided the survey ground control needed to resolve the airborne photogrammetry and develop a highly accurate point cloud. An LAS file of this data was generated and imported into the Leica Cyclone point cloud processing software. LAS is an industry-standard binary format for storing airborne LiDAR data. The two random traverses established by the WSP and all the terrestrial scan data they collected were also brought into Cyclone and transformed onto the common coordinate system using the positions established by the Leica GS14 rover. This approach provided a validation on both open traverses.
With data processing complete, the data from the UAV, the GNSS rover, and the ScanStation was successfully been combined with the quality assurance checks gathered throughout the process. The entire 800-yard-plus crime scene had been digitized from both ground and air to produce a single rich, detailed color point cloud.
Forensic Analysis and Admission as Evidence
Of key interest to the WSP Firearms Unit for the shooting reconstruction was the difference in elevation between the shooter’s position and that of the victim. This measurement was easily extracted from the point cloud using Leica Cyclone software, as was the height of and distance to the far riverbank that was supposed to serve as a backstop for the shooting party. Also produced for trial using Leica Cyclone were two vivid fly-throughs of the point cloud, which were created to provide investigators (and ultimately the jury) with a 3D visualization of the entire crime scene from the riverbank to the backyard.
On the morning of November 30, 2016, Whatcom County Superior Judge Raquel Montoya-Lewis ruled that a proposed prosecution witness employed by Leica Geosystems was qualified as an expert to testify in matters related to forensic laser scanning, photogrammetry, unmanned aircraft systems and the GNSS technology. Her ruling was made over the strenuous objections of Zylstra’s defense attorney, who wanted both the expert witness and the compelling evidence package created from Leica Geosystems reality capture sensors excluded from trial. The judge also ruled in favor of allowing the Leica Geosystems evidence package presentation to be shown to the jury, as well as both fly-throughs.
Later that afternoon, Whatcom County prosecutor Eric Richey called the expert witness to the stand, where he testified in front of the jury about the various technologies and workflows used. Both the evidence presentation and the fly-throughs were shown and used to help the jury understand the several technologies deployed and how they were brought to bear on the case. Jurors listened intently to the testimony, and the 3D visualizations gave them a real sense of the crime scene terrain in a way that 2D maps and photos could not convey.
Closing the Case
In December 2016, the jury found 34-year-old Nickolas Adam Zylstra guilty of second-degree manslaughter for causing the death of Alyssa Smith through criminal negligence. A judge sentenced him to five years and three months in prison. The case made against him came as the result of the hard work of the many dedicated Whatcom County detectives, prosecutors and Washington State Patrol forensic scientists who investigated the case. By using innovative and reliable reality capture solutions, the investigators were able to effectively map the complex crime scene and uncover the truth so justice could be served.
Author’s note: This article is dedicated to thememory of Alyssa Christine Smith. We are grateful to her family for giving us approvalto publish this account.
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