WAUKEGAN, Ill. (AP) _ A judge today found a man guilty of first-degree murder in the sulfuric acid poisoning of his infant son in what prosecutors said was a scheme to sue a commercial baby formula manufacturer.

Ricky Irby Sr., 29, could face the death penalty. Lake County Associate Judge Harry Hartel, who presided over a two-week, non-jury trial, set a sentencing hearing for June 29.

Irby and the child's mother, Sheila Smith, both were charged in the death of Quinten Irby. The infant, who was 3 months old when he was force-fed sulfuric acid May 31, 1984, lived for 27 months at Children's Memorial Hospital in Chicago. He died Aug. 26, 1986.

Ms. Smith already has pleaded guilty in return for a 20- to 65-year prison sentence.

Irby's attorneys contended that the father had nothing to do with the crime. Prosecutors contended that the couple poisoned the baby with the intent of suing a baby formula manufacturer.

At one point, the case was essentially closed when evidence, which had been tested by a toxicologist, was discovered missing. Later, investigators determined that a lab clerical worker accidentally destroyed the evidence.

The case was reopened after a U.S. Supreme Court ruling in November 1988 that said evidence lost by accident does not preclude prosecution.