my son was just arrested for a 211 they picked him up while walking down the street they told him that the det?

Wanted to question him .he said when he went to the police station .the detective told him if he was incolved in a 211 my son told them he didnt no what they were talking bout my son said they were telling him he was gunna get a serious of time so he suld just admit it.he said he was so scared he just told them ok i was he said they never had a witness they lied