McCarthy was accused of killing 2-year-old Bella Bond in 2015, the daughter of his former girlfriend Rachelle Bond.
After 15 days of testimony, the defense rested its case on Monday morning - without Michael McCarthy taking the stand.
When the 2-year-old's body washed ashore on June 25, 2015, investigators dubbed her "Baby Doe" as they launched an worldwide search for her identity.
On Friday, they called a woman to the stand who met Rachelle in a clinic and contacted police about a possible connection between Rachelle and the then-unidentified body of a little girl who washed up on Deer Island.
McCarthy has pleaded not guilty, and defense attorney, Jonathan Shapiro, has told jurors that Rachelle Bond is the actual killer of the child. They began calling witnesses Friday and they may wrap up Monday.
Bond pleaded guilty to being an accessory after the fact to murder in February.
Prosecutors allege that Bella had been abused before she was killed, and McCarthy murdered her because he thought she was possessed by evil spirits, according to People. The conversation and the photos prompted her to call police.
"She was a demon anyway, it was her time to die", McCarthy allegedly told Bond when her daughter was found dead.
Jurors on Thursday heard McCarthy's recorded interview with police in which he denies killing Bella.
McCarthy, 37, faces life imprisonment without parole if convicted of first-degree murder.