My mother called and says Michelle's dead.

How is that possible?

A young mother found brutally murdered her little girl

left to wander in her mother's blood.

Police had a suspect, and they say he had a motive.

We had an intimate relationship.

You ended up having sex?

But could they prove he was the killer?

It was a circumstantial case.

Except for that witness, the girl who left those footprints.

We will never know what Cassidy saw and what she didn't see.

Maybe she couldn't tell detectives who the killer was,

but maybe she didn't have to.

The fact that Cassidy was spared,

would that mean anything to a jury?

The person that killed the mother cared about Cassidy.

And now a stunning twist in the case.

I'm Lester Holt, and this is Deadline.

Here's Keith Morrison with Silent Witness.

I think I paused for a second.

I had to take a deep breath,

and just the reality of what was going on, saying can't.

...