What do you think?

So about a year ago i rescued my puppy Riko. He was a frequent flyer i was told at the shelter. He was known for darting out and running from his owners. As we walked around there were only 3 dogs in the kennels. They were all older and wouldnt fit for my young kids. Riko was outside. We walked out and he came runnin to us but never jumped on my kids. Tought that was a good sign. He was very playful and played fetch. When we decided to take him his paperwork said boxer mix. He is very loyal and has been great with us. My question is, what do you guys think his breed is? He has black with a white chest but brindle under the black you can see when the sun hits it. I just cant see boxer because his jaw isnt boxer like. He looks alittle pitbull to me. What do you all think?