Here's why:
* Melissa's alibi: Melissa had a solid alibi for the night Alison disappeared. She was with her then-boyfriend, Ian Thomas, at a party.
* Melissa's actions: While Melissa initially lied about her whereabouts, she later came clean and cooperated with the police.
* The true killer: The identity of the killer was revealed later in the series, and it was not Melissa.
The answer to your question is no, Melissa did not kill Alison.
However, it's important to note that:
* Melissa was involved in a number of secrets and shady dealings throughout the show.
* She was initially suspected by the Liars, and her actions contributed to the mystery surrounding Alison's disappearance.
The identity of Alison's killer is a significant plot twist in "Pretty Little Liars" and is worth exploring further if you're interested in the show.