Setting: Modern day Earth, no special technology advancements.
Situation: On day, in a relatively populated American city (the specific city is unimportant...the purpose of this point is that it's high-visibility), an apparent nuclear explosion occurs and absolutely levels several blocks.
Video footage recovered from streamed cell phone footage (all storage devices in the area were destroyed) at the time of the detonation shows that it originated out of thin air, about five feet off the ground, in the middle of the street.
The destruction is almost absolute within the radius of the explosion, with almost everything pulverized to dust and/or incinerated.
However, in the dead center of the crater, rests a mostly intact human arm. The skin is charred, but the tissue within is almost untouched. The arm ends just shy of the shoulder, cut cleanly at the molecular level; the cut is not charred/cauterized. The hand was found gripping a piece of paper, charred beyond legibility.
Additional Info: Unknown to people in the present, the arm belonged to someone from about 500 years in the future.
Question: Given the full focus of the global scientific community, and all the resources America and its allies could bring to bear, what could we learn about an arm in that condition?
Assume there are no implants within the arm, its former owner had no artificial genetic modifications, and that the fingerprints and fingernails were burned off. Also assume that it took twelve hours for the arm to be retrieved and placed in cold storage.
The arm was charred by external heat of about 2,000 degrees Celsius, rather than the 100,000,000-degree temperature of the apparent nuke. There was no radioactive fallout from the explosion, and the arm has suffered no radiation damage (beyond that experienced in day-to-day life).
Specifically, would we be able to determine that it's not from our time? Would the intact blood, bone, and muscle tissue allow us to guess at the diet, age, gender, or even occupation of the person it was once attached to?
Would an adult's arm, after being detached for twelve hours, still contain intact DNA to sequence? Would the blood still be viable for analyzing the white blood cells (ie, to determine immunities)?
I'd like to stick to concepts grounded in present scientific/technological understanding, but I'd be open to including speculative technology which may reasonably be invented within a year, in direct response to such an event.