Nephew staying with us and leaving what seems to be pieces of cut off skin over one of my daughter's belongings.

I'm having my 19 years old nephew over while his parents sort some stuff out, he's been with us for three weeks and has been displaying some odd behavior towards my 14 years old daughter. He seems to have some hatred towards her but he doesn't show it on front of my wife or I, it seems to happen only when we're not looking. When he's with us he's very well behaved and helpful around the house, but what we see doesn't fit with what our children are telling us is happening.My daughter told me my nephew has been leaving piles of what we think is pieces of skin -that he must have cut from somewhere- over her stuff. This morning she woke up and there was a small pile over her tablet case -we took a photo-. When we confronted my nephew this morning he said our daughter was making it up to pit us against him, but our daughter has a record of not lying to us and we have complete trust in her, plus like she well pointed out, she didn't have skin missing.Wth does this mean? This is some disturbing behavior but the situation is bizarre because we haven't seen him do anything to our children. We have 4 children (3 girls- 16 months, 9 y/o and 14 y/0) and a boy (24 y/o) . They all say our nephew is cussing, taking their toys, provoking them and just whats seems like normal teens behavior to us but the way they're telling is like my nephew is acting our of malice and with the intent of hurting them. We caught him wrestling with out daughter and she was crying, he said it was just playing but she said he was actually hurting her. We sat him down and told him we don't accept that behavior in this house, he's older and bigger than her and it's not ok to play-fight after she asked him to stop repeatedly.After that happened she complained he seemed to be going after her, but my wife and I haven't witnessed any particular behavior indicating he's targeting her. He 'accidentally' broke two of her favorite toys she had kept from when her childhood, which both my wife and I agree he seems to have done it on purpose because our daughter told us he was smoking in the garden. Since that happened he's been leaving small piles of what really seems to be skin on her belongings -on top of her uniform, over her pillow, on her tablet case this morning-.What does this mean? This is not normal behavior for a 19 y/0. I called my brother and asked him to come get his son because thing are not working out here with us. He'll be here on Friday but we're a bit freaked out and don't feel comfortable having him around our children. via /r/Parenting http://bit.ly/2R5Z5Nb