A not-guilty plea was entered Friday for 19-year-old Latrez Cummings. Like the other adults in the case, Cummings is charged with assault with intent to murder and assault with intent to do great bodily harm.
A 16-year-old is charged as a juvenile with assault and ethnic intimidation in the case. He faces a hearing Saturday.
They are accused in the April 2 attack on 54-year-old Steve Utash after he stopped to help 10-year-old David Harris. Harris was struck after stepping into the path of Utash's truck.
Utash, a tree trimmer from Clinton Township, remains hospitalized with severe head injuries. The boy suffered a broken leg and other injuries.
Police said the mob might have killed Utash if not for the actions of Deborah Hughes, a nurse who saw the accident from her window and rushed to help the boy before turning her attention to shielding Utash from his attackers.
Detroit Police Chief James Craig has said their investigation into the beating is widening and more arrests could be forthcoming, reports CBS Detroit.
Because Utash is white and the mob was described as all black, many - including Utash's son - have questioned whether the attack was racially motivated. But officials say that's not necessarily the case, according to the station.
"In the case of the four adult defendants that have been charged, the facts and the evidence do not support a charge of ethnic intimidation," Wayne County Prosecutor Kym Worthy has said.