According to the National Association of Medical Examiners, acceptable samples for post-mortem DNA analysis include: blood, tissue, bone, or hair.
The Australian Journal of Forensic Sciences published a study in 2019 comparing the quality of 320 postmortem DNA samples collected using buccal swabs vs. blood. This study showed that “Full DNA profiles were obtained from all blood samples.” while “...18.7% of buccal swabs yielded partial profiles, while 6.7% failed completely.“
For these reasons, buccal swabs are not recommended for post-mortem samples.
Furthermore, it is important to note that any cleaning agents used to sterilize/sanitize the mouth will destroy any remaining DNA. In order to provide high-quality DNA back to the family, our collection kits include supplies to collect tissue and hair. Our tissue kits are optimized for a quick collection - it takes about 30 seconds to obtain a small, pea-sized amount of tissue with our supplies.