The outlet reported Fattorini overdosed on a combination of alcohol, cocaine and GHB (gamma-hydroxybutyrate), the last referred to as a "date rape" drug.
Fattorini's parents claimed Merriman showed up to a club promoter's house party their daughter attended "and was allegedly witnessed carrying a bottle with some sort of liquid inside."
Per the lawsuit, it is alleged Fattorini texted a club promoter, writing, "you friend just poor'd half G in my drink." According to TMZ Sports, Fattorini's parents claim "G" is GHB.
The lawsuit further alleges that first responders found an unresponsive Fattorini "half-naked with her jeans unzipped and unbottoned" following a 911 call.
A preliminary report from the autopsy did not reveal foul play, per the lawsuit.
According to TMZ Sports, "a test for sexual assault because officials said it wasn't conducted at the time of the initial autopsy, and couldn't be done properly afterward."
The parents also claim to have read two texts between the promoter and one of their daughter's friends.
"Shawn killed her ass, what a f---ing idiot," the alleged text from the promoter read.
The other alleged text from the promoter claimed "that dumbass been drugging girls for years."
Per TMZ Sports, the "complaint claims negligence, battery and a violation of the drug dealer liability act," and the Fattorinis are seeking damages.
A representative for Merriman provided a statement to TMZ regarding the allegations.
"As of right now Shawne, nor his attorney, have any knowledge of him being named in any lawsuit. This alleged lawsuit is baseless. Shawne attended an after party more than two years ago where a young woman unfortunately overdosed," the statement reads.
"The police thoroughly investigated and found no wrong doing whatsoever by Shawne. The fact that they are raising this now, two years after the fact, demonstrates the baseless nature of these allegations."
ProFootballTalk's Mike Florio countered the representative's claim that the allegations are baseless due to the timing:
"Actually, the fact that the lawsuit was filed two years after the fact shows merely that the lawyers decided to wait until the eve of the applicable statute of limitations to file the lawsuit; the delayed filing is irrelevant to the merit of the lawsuit or lack thereof," Florio wrote. "It’s possible that the lawyers tried to resolve the case without filing suit, recognizing that keeping claims like this from ever becoming public has value when it comes to determining a fair settlement amount—and waiting until the last possible moment to make the allegations formal and public.
"It’s not surprising that Merriman and his lawyer aren’t yet aware the lawsuit was filed. There’s usually a lag between the filing of a lawsuit and service of the summons and complaint on the defendant. If, as TMZ.com reports, a lawsuit was filed, Merriman will be getting a copy of it soon enough."
Merriman played in the NFL from 2005-2012 for the San Diego Chargers and Buffalo Bills.