LAWRENCE, Mass. – Constantine Pitsas wanted to give the guests at his cookout nothing but the best. But his good intentions led to a tragic mix-up that left the infant son of a friend dead from arsenic poisoning and Pitsas facing prison time.

On Thursday, Pitsas was acquitted of involuntary manslaughter and assault charges in an emotional case that left both sides visibly shaken.

Pitsas, 77, a retired dentist, thought he was reaching for water drawn from a natural spring when his financial adviser asked for water for his 4-month-old son’s formula. He actually gave Benjamin Glynn arsenic-laced weed killer. The baby died, and his 2-year-old sister, Morgan, suffered serious injuries after she took a few sips of the liquid.

During the three-day trial, Assistant District Attorney Gerald Shea said Pitsas’ conduct was “wanton and reckless.” He should have noticed a warning label taped to the handle with the word, “arsenical,” Shea said.

But Pitsas’ lawyer, James O’Shea, called the poisoning a “tragic accident” and said Pitsas’ conduct was not criminal. He said the label on the jug was not conspicuous because it was folded over and taped to a handle on the top of the jug.

Judge Patrick Riley said prosecutors had not proven beyond a reasonable doubt that Pitsas had acted in a “wanton and reckless” manner. Pitsas had waived his right to have a jury decide his fate.

“Sympathy for the untimely and tragic death of a four-month-old infant or sympathy toward an elderly man charged with these offenses have no place in this court’s consideration of the evidence and the determination of guilt or innocence of the accused,” Riley said in delivering his verdict.

Benjamin Glynn’s parents, Sonja and Douglas Glynn, held hands tightly as the verdict was announced, then rushed out of the courtroom after the judge read his decision. The couple was escorted to their car by state police. Mrs. Glynn sobbed as the couple left.

Pitsas shook his lawyer’s hand and appeared tearful as he hugged his wife after the verdict was read. He faced a maximum of 20 years in prison, if convicted.

Shea declined to comment.

The children and their parents attended a cookout given by Pitsas at his Nahant home on Aug. 9, 2003. Shortly after they arrived, Douglas Glynn asked Pitsas for some water.

Glynn testified that Pitsas reached for a plastic gallon jug near an outdoor table he had set up for food and drinks. Both children became violently ill within minutes.

Glynn described a frantic race to the hospital as the children repeatedly vomited and his wife sat in the back seat trying to help them.

Fitchburg attorney Edward P. Ryan Jr., who was not involved in the case, said Pitsas’ conduct did not rise to the level of “wanton and reckless,” as defined in the state’s manslaughter statute.

“This guy was negligent. But wanton and reckless conduct is different in kind and in degree from negligence and even gross negligence,” Ryan said. “It is conduct that amounts to the intentional disregard of known risks of serious harm.”

“He made a mistake, but making a mistake and being negligent is not conduct you can base a criminal conviction on,” he said.

Pitsas did not testify during the trial.

He told investigators that he had bottled water in a refrigerator, but decided it was too cold for the baby, so he got a container of what he thought was spring water.

The children first were taken to Beverly Hospital and later transferred to Children’s Hospital in Boston. When doctors discovered that they had ingested arsenic, authorities organized a high-speed interstate relay to bring the nearest supply of a rare antidote 240 miles from Eastern Maine Medical Center in Bangor, Maine, where members of a church had been treated four months earlier after they drank arsenic-laced coffee.

The antidote arrived too late to save Benjamin. Morgan, who authorities believe drank only a few sips of the liquid, spent 13 days in the hospital.