I'm in my 29th year of running in a relaively quiet town, but the following have been "witnessed" during my runs:
My college XC team smelled what later turned out to be the body of a missing man that was 10 feet from a country road.
I saw a car pull in front of a Harley that was going 50-55. The guy's head cracked like a melon and bled heavily in the road while I tried to comfort him, but he did not die until several hours later.
I've passed several couples engaging in sex acts.
I saw a deer get hit by a truck and fly about 100 feet through the air. After a couple of seconds it came to its senses and ran away.
During one of my late-night heat-of-the-summer college runs I saw 8-10 police cars swarm around a car driven by a gun dealer. I stopped and watched them pull several dozen guns of all types out of the trunk.
I saw a guy at a stop light beating the daylights out of his wife. His window was down, so I pulled him halfway out and beat him for a little while so as he could share in the hurt. Then I called the police.
I was attacked by dogs from two houses as once. The police and sheriff deputy both told me that, even though I fell in front of a car whose driver was quick enough to keep the wheels from rolling over me, I couldn't press charges because the dogs had not drawn blood. Note to self: get bit!
Recently, while running on a local college campus, I had several students jump out of a van and unload their airsoft guns on me.