The defendant says he was just jotting down some thoughts about a murder mystery he wanted to write. Prosecutors contend what was found on his computer disk was a 26-step plan for killing his wife.

Step 3: "Arrive at night, hide truck."Step 4: "Check on weight of cinderblock."

Step 15: "How do I kill her???"

Step 25: "Check in library on ways of murder - electricution (sic)."

Nobody has seen Marine Capt. Shirley Russell since March 4, 1989, and federal prosecutors say her husband, former Marine Capt. Robert Peter Russell, murdered her, although her body has yet to be found. His trial opened Tuesday, and he has pleaded not guilty.

Witnesses said Russell was a womanizer and drinker who showed an unusual amount of interest in his wife's life insurance policy just a week after he married her.

They said he also asked his fellow Marines about whether a television set in the bathtub would deliver enough of a jolt to kill somebody and unwittingly quizzed an FBI informant about how long it takes a body to decompose.

But the key piece of evidence, exhibit 19A, is a 51/4-inch floppy disk on which Russell stored a file labeled "Murder."

Assistant U.S. Attorney Lawrence J. Leiser said in his opening statement at Russell's trial that the defendant was concocting a "recipe for murder" when he created the computer entries.

Russell says the computer file was merely part of a mystery novel he was working on. He is free on $50,000 bond.

Sgt. Maj. William Joseph Kane said he found the computer disk when cleaning out Russell's office. The captain had been relieved of duty in February 1988, more than a year before his wife disappeared.

Most of the files on the computer disk were clearly military, but the one called "Murder" was among a few others that piqued Kane's interest. He said that in a telephone conversation with Shirley Russell a day later, he told her what he had found.

Shirley Russell, 29, disappeared from the Quantico Marine Base in northern Virginia, and despite intense searches, her body has not been found. Russell, 34, is being tried in U.S. District Court in Alexandria.