Next week, forensic analysts from all over the world will gather in Minneapolis for the 27th International Symposium on Human Identification (ISHI). So today, we’d like to share one story from a forensics lab that highlights the importance of collaboration, knowledge-sharing and technology development–since that is what ISHI is all about.
Crimes against children are especially heinous, and it is vitally important that the offenders are removed from the streets as soon as possible. In today’s blog, Sarah Chenoweth from the Anne Arundel County Crime Lab in Maryland describes a sexual assault case that was solved in just five days. Key to this speed were the collaboration between lab staff and state police, and the ability to quickly and reliably amplify DNA profiles from low-DNA samples. Thanks to the efforts of the investigators involved, parents in Maryland, and possibly nationwide, can sleep a little easier.
On Friday, February 5th, the Anne Arundel County Crime Lab was notified of a sex offense involving a 7-year-old victim. With our efficient DNA workflow, including use of the Fusion amplification kit with our 3500 Genetic Analyzer, we were able to identify the perpetrator in only five days.
Around 6:00 AM that Friday, a perpetrator reached into a child’s bedroom via an open ground floor window. He pulled down her clothing, and touched her inappropriately. Startled, the child woke and screamed, alerting her parents and causing the perpetrator to flee. She was able to provide a description of the assailant: a white male, adult but fairly young, with a tattoo on his arm.
Anne Arundel County Police promptly canvassed the apartment complex where the victim lived, and discovered a man matching the perpetrator’s description had attempted to break into a nearby apartment building at approximately 7:00 AM that same morning. When confronted, the man fled, dropping a pair of purple single-use gloves.
As a small lab of with only three analysts, including our Tech Leader and CODIS Manager, the Forensic Biology Unit is usually open only during weekdays. Fortunately, Anne Arundel County sees relatively little violent crime compared to neighboring jurisdictions. But for a crime like this, with no additional information about the perpetrator’s identity and given the very young age of the victim, one of our analysts was willing to come in early on the Saturday morning to start examining the evidence.
On Saturday morning, our Evidence Collection Unit submitted the purple gloves and Sexual Assault Evidence Collection kit from the victim. They also provided a reference swab from a suspect who lived nearby, who had several prior burglary arrests. The SAEC kit tested negative for any probative fluids, which was what we anticipated based on the details of the assault. Fortunately, the purple gloves proved more promising from a forensic standpoint. In our experience, swabbing the interior and exterior of single-use gloves separately improves the odds of obtaining an interpretable DNA profile. All four swabs gave promising quantitation results, ranging between 150 and 800 pg/µl.
Based on our validation and experience with recent casework, we knew that samples this strong were almost certain to produce useful DNA profiles. The analyst set up our 3500 Genetic Analyzer for an overnight run. She returned to the lab on Sunday morning to mixed news: All four glove samples gave interpretable profiles, and all were consistent with coming from the same unidentified male. The suspect, however, was excluded.
Our CODIS Manager uploaded the unidentified male profile on Monday morning. She also gave our SDIS Manager at the Maryland State Police a call, asking her to expedite the CODIS search. We are fortunate to have a great relationship with our colleagues at the state police lab, and our SDIS manager knows we only ask for rush requests in critical cases, so she readily pushed it through.
Meanwhile, the detectives in our Sex Offense and our Child Abuse units continued their investigation. On Tuesday, February 9th, they submitted a reference swab from a second suspect. By the end of that same day, the analyst completed her second report: Suspect number two was also excluded.
On Wednesday, February 10th, our SDIS manager contacted us with the news we’d been hoping for. The unidentified male profile produced two complementary hits: one to an arrestee’s reference sample collected in 2013, and another to a suspect’s reference sample collected in connection to a 2009 peeping Tom sex offense elsewhere in Maryland. The Maryland State Police had expedited their hit confirmation process, so we were able to give the suspect’s identifying information to our detectives right away. He was arrested the same day. Our laboratory confirmed the CODIS hit via an additional reference swab submitted a few days later.
The young victim’s description turned out to be highly accurate: The perpetrator was a 26-year-old white male, with heavy tattooing on one arm. He confessed to committing both the sex offense and the attempted burglary on February 5th. In addition to the 2009 peeping Tom case, he was suspected of several others: so many, in fact, his mother had nicknamed him “Peeps” when he was a teenager. He is currently scheduled for trial this summer.
We credit our success in this case to many factors, but particularly:
- A streamlined workflow, which includes Qiagen extraction robots, a 7500 real-time PCR instrument, the Fusion amplification kit, and a 3500 Genetic Analyzer. We can process a rush case, from sampling the evidence to obtaining a profile, within one working day.
- Good working relationships between our lab staff, our investigators, and the Maryland State Police CODIS unit.
- The ability to rely on the Fusion kit to develop DNA profiles from relatively low-level evidentiary samples. We have come to expect useful profiles from items such as gloves, clothing, and firearms.
The Anne Arundel County (Maryland) Forensic Biology Unit includes Sarah Chenoweth (DNA Technical Leader), Ashley Hayes (CODIS Manager), and Emilie Dembia (Forensic Chemist). With a combined 25 years of DNA casework experience, they handle 400 cases annually for a county with half a million residents.
ISHI 27 will see more than 800 experts in forensic analysis come together to share knowledge on the latest advances in DNA-based identification techniques. Register here to attend, or follow #ISHI27 from 26— 29 September to keep up with the event.
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