Nursing Home Abuse - My father is not being taken care of properly

Ever since I chose the nursing home for my father to stay at, there have been signs that something is not right. At first I thought I was being paranoid but now I'm getting really suspicious.

One time he had a bruise on his head but he said he couldn't remember what happened. The staff told me he started to fall and hit his head against the wall. Another time his arm and elbow were hurting and sore. When I asked him about it, he seemed troubled and said he's just getting old.

He's not acting the way he normally does and seems to be losing a little weight. And I did notice that some of the staff there act like their annoyed by visitors stopping by. Overall it seems like the people staying there are not happy and there is a tense uncomfortable feeling there.

I'm looking at other nursing homes to move him to but at the same time, I'm concerned about the other elderly people there. How would I go about investigating this without outright accusing them of nursing home abuse?