speech delay or autism ??

hello i am concerned about my clostest friends' two year old son, i spend alot of time around both her and her son, and i have noticed some symptoms of autism. my question to you is: how would we distinguish if he has autism or is just a late talker? he doesn't use very many words and i've noticed a decrease in his over all "daily speech". he tends to take all of his toys out and organize them or line them up, and his lack of communication is causing tantrums, screaming and crying, even though "time outs" are working he still doesn't seem to be able to tell us whats wrong, why hes upset, or seem to understand why he was put in time out, he often just repeats the behavior, which leads to more tantrums, and another time out later in the day. he doesn't seem to follow simple instructions or seem to be able to tell you what he wants, needs or how he feels. how can we tell if hes not understanding what is being asked of him or if he understands but just doesn't want to comply.