New details have emerged in the Charlie Tan case.

According to court documents obtained by News 10NBC, federal officials say Tan's friend, Whitney Knickerbocker, was pledging a fraternity at Cornell University that Tan was part of when Knickerbocker bought the shotgun investigators believe Tan used to kill his father.

Investigators believe Tan asked Knickerbocker to buy the gun at a Cortland Walmart after he was denied due to his Canadian citizenship. Court papers say Tan was Knickerbocker's frat "big brother" at Cornell.

Jim Tan was killed in his Pittsford home in 2015.

Charlie Tan's murder charge was dismissed, but he's now facing federal gun charges.

His trial is set to begin on June 25 in Syracuse.