ORLANDO, Fla. -- Prosecutors in the trial of a teenager accused of murder played on Monday his taped confession to detectives.

The videotaped exchange is part of evidence in the trial against Michael Hernandez, now 18. The teenager is accused of killing childhood friend Jaime Gough at Southwood Middle School in 2004, when both boys were 14.

Miami-Dade police Detective Salvatore Garafalo took Hernandez's confession in 2004.

"When he got to class, some of his fellow students told him he had some blood on his shirt, and so he went to ask his teacher if he could use the bathroom to clean up," Garafalo said.

In the hours following the crime, Garafalo questioned Hernandez about how Gough wound up dead in a bathroom stall. When cornered with inconsistencies, Garafalo said, Hernandez came clean about how he lured Gough into the stall and violently attacked him.

"He had Jaime's back to his front," Garafalo said. "Michael had his knife already opened in his pocket. He pulled his knife out and he grabbed Jaime and he sliced his throat."

Defense attorneys will argue that Hernandez was insane at the time of the crime.

Witnesses called by prosecutors so far are apparently already poking holes into that theory.

"Unremarkable behavior. He responded appropriately to all my questions," Garafalo said.

"Did he ever go off target or off-tangent or start talking about things that were not responsive to your questions?" a prosecutor asked.

"No," Garafalo said.