Last year 23-month-old Dillon Ferrer was smothered in his crib.
The only witness to the crime -- his 4-year-old brother Lucas Ferrer -- says their foster father, Charles Forshee, did it.
Now the case has gone to trial.
By way of closed circuit television, the child has told jurors that Forshee "punched (Dillon) on his back - on his stomach - and on his face."
While the little boy clearly stated that Charlie Forshee killed his brother, he was confused when asked easy questions -- like who Dillon was, whether the Forshee's had a dog -- or toys for him to play with.
The children's natural mother Amanda DeBarre said that within hours of Dillon's death, Lucas "told me Charlie hurt Dylan."
"My son told not only me -- but everyone in the hospital, the paramedics -- you know, everyone - what he thinks he saw happen," she said.
Psychologist John Burruss says relying on a 4-year-old to determine what really happened has risks.
"The way their memory works and their emotional state at that age does not allow one to place a log of faith into what they're saying," he told Maher.
Complicating the child's credibility -- is the child's own alleged history of trying to suffocate other children.
Melody Ginn, a shelter worker said she had seen Lucas trying to smother his little brother. "I looked over and Lucas had his hands over the baby's nose and mouth."
But thus far Judge Joan Huffman has refused to admit that information into evidence and has ruled the little boy does know the difference between the truth and a lie.
If the jury agrees and convicts Charles Forshee, the man who's been a foster father to more than 90 children could spend the rest of his life behind bars.