Murder Cell

A student's plea for help on a school paper late one night had Digger arriving at his lab to help. But he was too late to save the boy because he lay dead on the lab floor. As Digger knelt beside him, checking his pulse, an armed security guard arrived, pointing a gun at his head and arresting him for murder.
He was transported to jail without regard to his plea of innocence, where Digger phoned a friend. Then he waited in a cold cell for FBI agent Watson to show.
Once Watson arrived, he had Digger released from his cell, but the judge ordered him to remain under house arrest while the investigation continued.
As the evidence grew, putting Digger's freedom in question, his team found a link to a huge human smuggling ring. No one realized how deep this ring would go, but they agreed to follow it until the top leader was captured and put away for life.
This investigation was intense and suspenseful as Digger wondered if he would spend the rest of his life in a prison cell. What was the link that started this dreadful murder charge against Digger?