Prosecutors say a former laboratory assistant was trying to kill members of an Omaha family with cancer when he poisoned them with a rocket fuel additive.

Steven Roy Harper, 28, was convicted Friday of two counts of first-degree murder in the deaths of a man and an infant in what Deputy Douglas County Attorney Samuel Cooper called the "first murder by cancer, ever."

Durane Johnson, 24, and his infant nephew, Chad Shelton, died in September 1973 within days after drining beverages containing dimethyl nitrosamine, a toxic rocket fuel additive found to have caused cancer in laboratory animals.

The two died of massive internal bleeding, and an autopsy showed that nearly all their liver cells had died.

Prosecutors charged Harper wanted to make them die slowly but apparently had misjudged the dose. Under Nebraska law, Harper could be sentenced to death in the electric chair.

District Court Judge James Murphy set an Oct. 26 hearing date for introudction of findings of a presentence investigation.

The jury also found Harper guilty of three counts of poisoning with intent to kill, wound or main, stemming from the same incident in which Johnson's 2-year-old daughter, Sherrie, and Mr. and Mrs. Bruce Shelton, the boy's parents, became seriously ill.