Suicide or Murder?
|Unsolved Case Aided by New Technology
By Deb Derrick
New manufacturing technology is helping investigators find more clues in an old but unsolved criminal case in Nebraska. A phone call last summer pulled John Bonsell, industrial systems technology, into the middle of a re-opened investigation by the Nebraska State Patrol into the death of an eastern Nebraska man. In an unusual application of rapid prototyping technology, Bonsell and his students created a replica skull that could be used for evidence in the case.
The 1966 death of Marvin Bonham, a Fort Calhoun resident, was originally ruled a suicide. The case was re-opened three years ago when new evidence was brought to the attention of investigators that seemed to indicate the possibility of foul play.
After the skull fragments were pieced together, the reconstructed body part was taken to the University of Nebraska Medical Center for a CT scan. The State Patrol then worked with Materialise, a Michigan-based firm, to convert the scan to an STL (standard triangulated language) file format.
Materialise knew we had the prototyping machine because wed bought our viewer software from them, Bonsell said. They suggested the State Patrol contact us to have the skull replicated. The State Patrol was surprised that this kind of equipment was in their backyard.
Investigative Services Lieutenant Chuck Phillips delivered the digital file to Bonsell on a Friday. The machine ran over the weekend and Phillips came back on Monday to pick up the prototype. The project took about 32 hours of machine time. Undergraduate student Ben OBrien and graduate student James Vigil assisted with the project.
Rapid prototyping machines use lasers to fuse powder or liquid into a solid, layer by layer, in a process called selective laser sintering. A vertical elevator system lowers each newly formed layer as successive cross sections are bonded one on top of another to form a part from STL file specifications.
The selective laser sintering process produces replicas within .005-inch tolerance levels, Bonsell said. For every 12 inches, we can be no further off than a human hair. Thats extremely accurate.
The replica skull was made from a powdered nylon blend called DuraForm. DuraForm is a ductile, stable, high-strength plastic that starts out in fine white powder form. The material is expensive, said Bonsell, but the rapid prototyping process typically saves manufacturers money because it eliminates costly design changes prior to production.
Preserving the Past:
The left side of the replica skull shows a large and a smaller hole, and the right side shows three other holes. The number of bullet holes appears to point to homicide as the cause of Bonhams death.
Bonhams body was re-interred in September. All evidence has been turned over to the Washington County attorney to decide if charges should be filed.
Bonsell said rapid prototyping technology has widespread applications in forensics and medicine in addition to manufacturing.
In criminal cases like this one, Bonsell said about the State Patrol investigation, the technology can be used to preserve evidence before it further deteriorates. Once its in digital format, its preserved forever.
Phillips also sees the potential of the technology to assist in other investigations. The prototype is something tangible that could be presented in a court proceeding. Its a valuable tool, he said.