Joh 9:2 And his disciples asked him, saying, Master, who did sin, this man, or his parents, that he was born blind? 3 Jesus answered, Neither hath this man sinned, nor his parents: but that the works of God should be made manifest in him.
Who sinned was the question and Jesus answered neither the blind man nor his parents.
If we know no other verses nor continue reading then the simple answer is no one committed sin. But through continued reading and knowledge of other verses we can grasp a deeper understanding to what Jesus was saying.
1Jn … for sin is the transgression of the law.
Rom 4:15 … for where no law is, there is no transgression.
Rom 5:13 … sin is not imputed when there is no law.
Joh 15:22 If I had not come and spoken unto them, they had not had sin: but now they have no cloke for their sin.
Luk 12:48 But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more.
Jesus did not say they were guilt free, only that they had not sinned. Through the previous verses we see that sin is the violation of a (known) law. But through nature we are shown ignorance does not protect the flesh, but we know according to the word that ignorance protects the spirit.
Joh 9:41 Jesus said unto them, If ye were blind, ye should have no sin: but now ye say, We see; therefore your sin remaineth.