What was Once Cold is Now Hot: Solving Cold Cases at the NYC Office of Chief Medical Examiner

Wednesday September 25th, 2019 // 11:15 am - 11:45 am // Oasis 1-2

Within the past 15-20 years, successful technological advances in forensic science have solved many cold cases.  This presentation will highlight how this was done.  Testing of crime scene evidence was once limited to serology testing for biological fluids, such as blood or semen.  After blood or semen testing was performed, the case was completed and the resulting comparison to possible suspects was limited.  Blood or semen testing did not have the power to individualize the source of the stains and did not have the ability to provide the statistical analysis needed to help gain convictions in the courtroom.  Today, we can associate these biological fluids to an individual through development of a DNA profile and can provide evidence to a jury within a statistical calculation that can positively associate someone to crime scene evidence.

Touch DNA and low copy number DNA testing procedures, both new technological advances in forensic science, have ushered in a new era of DNA testing.  No longer are large amounts of extracted DNA needed for DNA profile development.  It is now possible to obtain a DNA profile from only a few cells.  As a result, items that were merely touched by an alleged suspect can currently be examined, revealing a whole new realm of possible evidence left behind at a crime scene that can be considered for DNA testing in cold cases.  In addition, previously collected DNA samples can be reassessed with modern technology.  For example, evidence items such as a victim’s fingernails collected at autopsy, which would not have been examined for foreign DNA in the past, can now be examined and tested due the significant advances in the sensitivity of DNA testing.

The increase in the number of possible items that might presently be tested as evidence in criminal matters, in general, has led to the need for collaborative efforts among the New York City DNA Laboratory, the New York City Police Department, and the New York City District Attorney’s Offices.  A multiagency approach had already become necessary, in large part, due to the challenges faced in the processing of cold cases.  I will discuss the complexities in processing cold cases and provide information on how best to surmount them.  Challenges include legal considerations, such as chain of custody issues; practical considerations, such as strained resources; and technical considerations, such as how to work with contaminated and degraded DNA samples.  Funding and budgetary issues are also an issue.

Finally, in this presentation, I will present examples of successful cold cases tested in New York City, despite the existing constraints, and will highlight how advances in technology and a multiagency team approach have resulted in their resolution.  These examples will hopefully inspire attendees to start cold case units in their own agencies and realize that what was once cold can become hot.


Lisa Mertz

Criminalist Level IV, Senior Supervisor, Cold Case Liaison, OCME

Lisa Mertz has worked at the OCME in the Forensic Biology Department for approximately 14 years as a criminal casework analyst, supervisor, and cold case liaison.  She has written and technically reviewed thousands of casework files of various crime types and has testified as an expert witness over 70 times in all courts in all the boroughs of New York City.

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