Marriage Puzzle

Years ago, my sister-in-law rushed to help me pick up my son from kindergarten. But on the way back, there was a car accident. I lost my son, but my sister-in-law was unscathed. I watched the surveillance footage countless times. It was my son who let go of his sister-in-law's hand and ran to the road on his own. This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.