Valedictorian Accused of Killing Mother: Detectives Testify

University of Michigan student Jeffery Pyne is on trial for the murder of this mother.
3:00 | 11/21/12

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Transcript for Valedictorian Accused of Killing Mother: Detectives Testify
Let's turn to tuesday's explosive testimony in the case of that michigan valedictorian on trial for killing his mother. A lead prosecutor said point-blank, he thinks he is guilty of the crime. And john muller has all of the details this morning. Reporter: It was a con fontational day for the defense. I know who killed ruth pyne. Reporter: Jeffrey pyne's attorneys saying he couldn't know for sure who killed ruth pyne. You were in the garage? I was not in the garage. I'm basing my opinion based on the evidence as I know it. And that's my opinion. That's an opinion. Thank you. Reporter: But the prosecution wasn't about to let it end there. When it comes to his alibi, he lied about where he was at. He lied about what he was doing. Was I in that garage? I was not in that garage. But my opinion is that jeffrey pyne killed his mother. Reporter: The 22-year-old maintains he was at work all day when his mother was brutally murdered. But on monday, a paramedic on the scene testified he overheard pyne tell his faer, he saw his mother inside the house, less than two hours before her body was discovered. And that she was alive and well. I did hear jeffrey pyne say to his father that he was just at the house at 1:30. He was at the house at 1:30? Yes. Reporter: Detectives also told jurors that pyne's father noticed items missing from the family's garage. Two wooden boards, a screwdriver and a box cutter. Prosecutors contend pyne used the boards to beat his mother before stabbing her 16 times. Their evidence, striking blows to his case, all week. Many in this tight-knit community, hearing the gruesome details for the first time since his arrest last may. People in this community don't much care whether or not jeffrey pyne killed his mother. They are rallying around him. Reporter: This morning, pyne maintains his innocence. For "good morning america," john muller, abc news, new york.

This transcript has been automatically generated and may not be 100% accurate.

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