A 5-year study on DNA recovered from fingernail clippings in homicide cases in Milan

Frequency of biological non-skeletal materials in dry bone scenarios

In forensic anthropology, many small biological non-osseous materials may be found associated to skeletonized remains and can provide crucial information to the biological profile. Indeed, their careful recovery and correct identification can add information related to age-at-death, sex, ancestry, health, diet, migration and habits, and may be used in specific analysis such as DNA typing. However, and despite their potential, little is known about these non-osteological materials. Indeed, how frequent are they in dry bone cases? To answer this question, 100 skeletal remains with postmortem intervals ranging from 23 to 76 years from the CAL Milano Cemetery Skeletal Collection were meticulously examined for the presence of non-skeletal materials and in particular ossified cartilage, vascular calcifications, hair and nails. As a result, non-skeletal materials were found in 81 skeletal remains and showed high frequencies of recovery, despite the less-than-optimal conditions of exhumation of the skeletons. The high frequencies of non-skeletal materials obtained demonstrate the need for additional training and research given their informative power in forensic cases.

Male DNA under female fingernails after scratching: transfer and persistence evaluation by RT-PCR analysis and Y-STR typing

The collection of biological debris beneath fingernails can be useful in forensic casework when a struggle between the victim and the offender is suspected. In the present study, we set up a controlled scratching experiment in which female volunteers scratched the male volunteers' forearms, simulating a defensive action during an assault. A total of 160 fingernail samples were collected: 80 "control samples" before the scratching, 40 samples immediately after the scratching (t = 0 h), and 40 samples 5 h after the scratching (t = 5 h). The aim was to evaluate, using a real-time PCR approach and Y-STR profiling, the transfer and the persistence of male DNA under female fingernails after scratching. A significant reduction in DNA yield was observed between fingernail samples collected immediately and those collected 5 h after scratching, with a corresponding decrease in Y-STR profile quality. Overall, 38/40 (95%) of the fingernail samples collected immediately (t = 0 h) and 24/40 (60%) of those collected 5 h later (t = 5 h) were suitable for comparison and the scratched male volunteers could not be excluded as donors of the foreign DNA from 37 (92.5%) of the t = 0 h and from 10 (25%) of the t = 5 h profiles. The analysis of male DNA under female fingernails showed that Y-chromosome STR typing may provide extremely valuable genetic information of the male contributor(s), although 5 h after scratching the profile of the scratched male was lost in three-quarters of samples.