Sources tell TMZ Michael went to the Sheriff's Department and said 16-year-old Ali Lohan was staying with Lindsay and he was concerned for her safety.
Lindsay just tweeted she is angry at building management for letting the cops and Michael in.
Michael, we're told, convinced deputies to go to Lindsay's pad to do a "welfare check" on Ali.
We're told Ali was in the apartment and deputies spoke with her. Deputies left and Ali was allowed to stay with Lindsay.
We're told Michael is now going to the L.A. County Department of Children and Family Services, per the advice of the Sheriff's Department.
Sources say Michael made a "compelling case" to Sheriff's deputies -- we're told Michael told deputies Ali was in Lindsay's car on the way back from Coachella and the car was going over 100 mph.
We're told Dina Lohan wants Lindsay to get a restraining order. Problem is ... Michael had the legitimacy of the Sheriff's Dept. behind him, so it's unlikely a judge will see it Dina's way.
We just shot video of Michael leaving the Sheriff's Department in West Hollywood.
Dina Lohan just told us, "I was told by my attorneys not to speak because it is very serious and my ex could be in big trouble. He's dangerous.... If he can't get to them he is going to try to hurt them -- it's not good."