The Mount Pocono resident had celebrated his 21st birthday just days before Upper Mount Bethel police found his locked Chevrolet Monza at the Delaware Water Gap's Arrow Island Overlook off Route 611, according to troopers.
In an archival report from the Allentown Morning Call, authorities said Gross was found in the back, under a tarp in a pool of blood just after 1 a.m. on Aug. 11, 1977.
He had been strangled and beaten "about the head and body," and a short rope ("the kind used with pulleys on exercise equipment") was found snugly tied around his neck, the newspaper reported.
Detectives do not believe the 21-year-old was killed at the overlook — no signs of struggle or weapons were found at the scene — but have speculated Gross was "murdered at another location and transported" there.
Citing a then-state trooper, the Morning Call report suggests he might have been robbed before his murder.
His killer or killers may have been present at his final birthday celebration in Cresco, which "was heavily attended by people from the Pocono Mountain and Lehigh Valley areas," and had "several bands (...) hired to play at the event."
Gross, police noted, was a 1974 graduate of Pocono Mountain High School, was employed at his father’s carpentry business, and had just started working for a local art gallery.
The Pennsylvania Crime Stoppers renewed their request for tips in Aug. 2023. Tips that solve this cold case or lead to an arrest could be eligible for a $5,000 cash reward.
Anyone with information is urged to call Pennsylvania Crime Stoppers at 1-800-472-8477), or submit a tip online.
Click here to follow Daily Voice Lancaster and receive free news updates.