FBI gets tip from Utah witness. SERIAL BOMBINGS

Federal Bureau of Investigation agents hope that an eyewitness account of a bombing in Salt Lake City will help identify the person they suspect is responsible for at least 12 unsolved bombings nationwide since 1978. According to FBI spokesmen, a major break in the serial bombing case came last Friday when a white male with reddish-blond hair and a light mustache was seen planting a package, which turned out to be a pipe bomb, behind a computer sales and service company in Salt Lake City.

An hour later the bomb exploded, injuring a company employee when he tried to pick it up in the firm's parking lot. An examination of the remains of the bomb showed similarities with 11 previous unsolved bombings, federal investigators say. No motive has been established.

The explosive devices are described as gunpowder pipe bombs that are packed with nails and screws to provide additional shrapnel. They have been disguised as packages and are set to explode when moved.

The description that resulted in a composite sketch of the man thought to have planted the Salt Lake City bomb was given by an employee of the computer store to federal investigators.

It is the most detailed eyewitness account federal invesigators have received since beginning the investigation nine years ago. According to the FBI, the man is white, age 25 to 30, and 5 feet 10 inches to 6 feet tall. At the time he planted the bomb, the man was wearing blue jeans, a hooded sweatshirt, and aviator sunglasses. Authorities think he still may be in the Salt Lake City area. They are hoping that residents who may have seen him will contact a special federal task force.

The serial bomber is said to have twice sent letters to the targets of his bombs. On four occasions he actually mailed bombs disguised as a manuscript, a notebook, or a book to his intended victims.

FBI agents say computers appear to be a common element to each bombing target. They say the serial bomber has targeted computer stores, university professors involved in computer classes, and commercial airlines, which use computers. But the agents stress that no specific pattern has emerged. The attacks have led to 21 injuries and one death.