Water in the trunk. Can’t figure where the leak is

My stepson's 2003 Neon's trunk fills with water everytime there is a rainstorm. The trunk rubber weatherstrip appears to be in good condition and is mounted correctly. The trunklid fit looks good as well. The cat has a factory-installed spoiler. I am kind of at a loss as where the water is coming in from. I will appreciate any ideas or tips. Thanks.
Author: tdzik