Using a bra identical to the one Kercher wore, Comodi strapped it to a microphone and pulled it with a finger to show how Sollecito allegedly pulled it back so he could slice it off, and leave his DNA on the clasp.
Sollecito's lawyer has argued that the clasp wasn't found for 43 days and in that time Kercher's room was thoroughly searched and items moved around. During the extensive search, the crime scene and possibly the bra clasp were contaminated, they stated.
But police forensics experts can tell when evidence has been contaminated and the clasp was not contaminated, Comodi said.
She also countered the defense's claim that Knox and Sollecito did not act like killers when they called the police after finding Kercher's body.
"The perpetrator of a crime is known to give the alarm in order to avert suspicion from himself," a mechanism that does not require a criminal mind, she said.
Comodi closed the prosecution's case by comparing the stories of Sollecito, Knox and the prosecution to the children's story TheThree Little Pigs. Sollecito and Knox built flimsy stories of straw and sticks, she said.
"The third house, solid, and built brick on brick, is the prosecution. Not even one piece of the puzzle is missing," she said.
A lawyer for Kercher's family also spoke to the jury today, asking them to convict Knox and Sollecito of murder.
Francesco Maresca said he wanted to "remind the jury one more time that we are speaking of a victim who was just a 21-year-old girl found dead at the hands of young people of her own age."
He said that logic pointed to Knox and Sollecito as the killers who had already sexually assaulted Kercher.
"Meredith died because after having being attacked, threatened, and sexually assaulted, they had to silence her in some way, and you get that silence with death," he said.
Maresca said that after the long trial,all of the jurors doubts should have been removed.
"You must have certainties. Doubts belong to an earlier phase," he said.
If convicted of murder, Knox could face life in prison. She is simultaneously being tried in a civil suit in which prosecutors are asking for $12 million in damages for the Kercher family.
In addition, she is being tried for slander because in an odd confession during an all night interrogation she told police she had a vision of being at the crime scene that night and that a bar owner, Patrick Lumumba, was also present.
Lumumba was arrested, but later cleared. He has sued Knox for defamation. Conviction on that charge could result in a six year prison sentence.
Knox has since retracted the statement and said it was made under duress while police were treating her aggressively and even hit her on the back of her head.
ABC News' Nikki Battiste contributed to this report