From Wikipedia
The Witness is an interactive fiction computer game written by Stu Galley and published by Infocom in 1983. Like Infocom's earlier title Deadline, it is a murder mystery. The Witness was written in ZIL, which allowed it to be released simultaneously on many popular computer platforms including the Apple II and the Commodore 64. It is Infocom's seventh game.
The game takes place in Cabeza Plana, a quiet (and fictitious) suburb of Los Angeles, California in February 1938. Freeman Linder, a local millionaire, has begged the police for protection from a man named Stiles. The player's character is a detective assigned one evening to check out the wealthy man's claims.
Is Linder seriously in danger or just another rich eccentric? Before the player can decide, a window explodes and Linder collapses, dead. The case of possible harassment has just become a murder, with the player as the only living witness. With the help of Sgt. Duffy (last seen in Deadline), the player has until sunrise to solve the mystery. As usual, motive, method and opportunity must all be established to secure a "solid" arrest and the optimal ending.