River Rock
In December of 1995 rocks were used to brutally bludgeon a young 17 year old girl named Krystal Beslanowitch. Her body and the rocks were found next to the Provo River that cold December morning. Despite the best efforts of the investigators and because there was limited evidence, the case quickly went cold.
Fast forward 18 years to 2013. DNA processing equipment in the crime lab had gone from requiring large samples to just a few cells, but traditional collection methods still failed to collect enough DNA material to produce a viable DNA profile. Fortunately the investigators also had access to a new collection method, the M-Vac™ System. 
They used the M-Vac™ to vacuum the suspect's DNA from the rocks. Where other methods had failed to produce anything meaningful, the M-Vac™ collected 21 nanograms (ng) of DNA material. It is interesting to note that the lower threshold for a full single profile is about 0.1 ng, which makes 21 ng so significant. The collection resulted in a full profile. The profile was critical in moving the case forward and bringing it to a conclusion. The suspect was found and arrested. Three years later in September of 2016, the trial was conducted and concluded with a guilty verdict.
In a September 2022 episode of his All Things Crime podcast, Jared Bradley did a very interesting and thorough recap of this crime and its resolution, filmed on site at the crime scene. To watch the half-hour podcast, click here.
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References:
sltrib.com September 30, 2016
sltrib.com September 25, 2013