Detecting Horse abuse?

I Ride/care for and 11 year old warmblood cross. He spooks very easily and is very wirey around people and new objects such as jumps hoses and whips. My trainer and I have recently descovered some signs of past abuse. Such as random scars, odd markings on his hind legs, back, etc. He has weird moods that he gets into sometimes he gets really high and crazy and other times hes very quite and slow. He normally calms down when you give him treats and affection. Today when I arrived at teh barn he was calm but after he was tacked I walked away for about 2 minuets and when I can back he wouldnt let me come near him. If i walk towards him he oulled his head up and tried to back away from me. It took about 10 minuets before I could calm him down enough to bring him into the ring. Once I got on he calmed down a lot. It was the first time he has ever "freaked out" with me I knew when I first started workng with him that he got scared easily and my trainer and I were very suprised to see how quickly he started to trust me. I have been working with him for a little over a year and to this day he has never buck or bolted with me riding him. (he does this very often with other riders) We have created a strong bond over the last year and it was scary for me today to see how quickly he became scared of me. After I rode I spent about 2 hours with him. (i hosed him, grazed him and played with him) just to make sure he still trusted me and he was perfectly fine. My trainer asked me to go home and research some signs of abuse so we can find out what really happened to him in the past. If you know anything aobut abuse and the effect it can have on the horse in the future please respond. Everything helps .