The photojournalist was called to the stand in Los Angeles on Friday (16Oct09) to give evidence to determine whether Stern and the actress/model's doctors Khristine Eroshevich and Sandeep Kapoor acted inappropriately in furnishing the tragic star with drugs.
Birkhead told the court his late ex-girlfriend took more drugs than anyone he'd ever seen and that he'd attempted to warn Smith's medics her substance abuse was spiralling out of control.
He returned to complete his testimony on Monday (19Oct09) and revealed how the Deputy District Attorney, Sarah Slice, had attempted to bully him after Friday's court session when his testimony appeared to show support for Stern.
He also claimed Slice had tried to suggest his daughter with Smith, Dannielynn, had suffered developmental problems as a result of the tragic beauty's drug use during her pregnancy - claims Birkhead denied.
Outside the courthouse, the photographer told reporters, "When people start talking about Anna and her medical situation and possibly my daughter's medical situation... that gets a little crazy and hazy, and it's like, what's the relevance? I think they (the prosecution) got off point several times.
"I guess I was there for the prosecution, they called me, but I don't know if they liked what I had to say, so I feel like, in turn, they were trying to beat me up in the end.
"There were some crazy things said to me that I felt was inappropriate (sic). Nobody in that courtroom knows about my daughter. My daughter's very smart, she's very happy, she's advanced for her age and yes, I did have concerns..., but I've been told by several doctors that she's quite advanced."
The hearing continues. Stern, Eroshevich and Kapoor have all pleaded not guilty to any wrongdoing.