Freeman, a West Paterson resident who graduated from Passaic Valley High School, had worked at Hoffmann-La Roche for about three years, Snack said. On a Saturday afternoon — Aug. 31, 1968 — she was working overtime in a second-floor office in Building 34, recording employees' hours from time cards.

Her killer came at her from behind, striking her in the back of the head with a wooden mallet. Time cards flew out of Freeman's hand like confetti, scattering across the floor. Her attacker struck her repeatedly in the face, then cut her throat. A guard making a routine sweep of the building found her body several hours later.

Snack said Freeman had been "triply killed," meaning any of her wounds would have been fatal. "It was just a brutal murder," Snack said. "She didn't deserve to die that way."
There isn't much info out there about this very old cold case, but I did find a couple of interesting tidbits. Buried deep on this page (use Control+F to find Joan's name), there's a post by someone claiming to be a relative, giving a little info about the Freeman family in the aftermath of Joan's murder and a short list of possible suspects:

Also, Joan is allegedly a ghost, haunting the place where she died: