My sister's ink-stained hand. Any advice?

One recent morning we found that the left hand of our sister (who was in AL under hospice care) was stained with a black ink-like substance. As if someone had used it to make a handprint/fingerprint. We had 24/7 caregivers and she had a caregiver with her that night and in the morning we found her hand this way along with a very dirty undergarment (diaper) and pad underneath a clean diaper and pad. The morning caregiver helped us clean her up, but the smell was unmistakeable (she was only 3 days from her passing and the urine was very dark) and we were concerned about what the night sitter had done...both with staining her hand with a dark substance and covering up the dirty underclothes with clean toppings.

We thoroughly checked her bed (she was bedridden, not able to get up -- she had multiple myeloma and was hardly able to turn from side to side without excruciating pain) and couldn't find anything there that would stain her hand.

I wonder if any of you all have an idea of why someone would take a handprint of a person near death...and what they would do with it. My sister was on methadone and they changed it to morphine the day before this happened, but it was being administered by the AL facility.

Thank you so much for your thoughts,
Toonces