Nearly 58 years after he repeatedly hit 10-year-old Betty Lou Zukowski with a rock and dumped her in a in West Springfield river, Donald Mars pleaded guilty to manslaughter Thursday morning, Hampden DA Anthony Gulluni announced.

“After 57 years, 11 months and six days, we finally have answers regarding the tragic, untimely death of 10-year-old Betty Lou in 1966,” Gulluni said at a press conference Thursday afternoon. “Through the diligent efforts of many people, Donald Mars pled guilty today to the killing of Betty Lou Zukowski on the river bank of the Westfield River in the town of West Springfield on May 26, 1966.”

Donald Mars, 75, of Bedford, changed his plea to guilty on the charge of manslaughter at a Hampden Superior Court hearing Thursday morning. Mars was previously indicted by a Hampden County Grand Jury for his involvement in the young girl’s death in November 2022.

Mars was sentenced to two and a half years in prison followed by two years of probation and registration as a level 3 sex offender. Much of his sentence has already been served during his years in custody, Gulluni said.

Both of Betty Lou’s parents are deceased, but two of her cousins attended the press conference Thursday and offered victim impact statements.

On that day in May of 1966, the DA stated, Betty Lou received a phone call that she told her mother was from one of her girlfriends and left the house around 6 p.m. Her family never saw her again.

After she failed to return home later that evening, her parents Stanley and Mildred Zukowski reported her missing to the Chicopee Police, the DA said.

After a four day search, two young boys fishing in the Westfield River found her “beaten and mud covered 4’ 7”, 75 pound body,” the DA’s office said. The medical examiner determined her cause of death to be multiple blunt force injuries to her head, a skull fracture and terminal drowning.

The West Springfield Police Department conducted a joint investigation with multiple local and state departments that went cold — searching the river and interviewing people in her life, the DA detailed. One witness in the initial investigation, believed to be the last person to see her alive, helped create a sketch of a man with her that day and described his “college-type” ring with a blue stone, but no suspects were identified.

During a renewed investigation between 1994 and 2001, the DA said, West Springfield Police linked Donald Mars to the killing. Mars was 17 years old in 1966.

In 1997, one witness pointed to two photos in the Chicopee Comprehensive High School yearbook similar to their recollection of the suspect, the DA said. One was of Mars.

Mars’s mother, then 95 years old, told investigators her son had admitted to throwing a rock and killing a little girl, the statement said. His ex-wife told of his multiple nervous breakdowns and two confessions — one in front of his parents — that he killed Betty Lou with a friend.

No arrests were made.

In June 2021, the Hampden District Attorney’s office’s Unsolved Homicide Unit picked up the case again, the DA said, re-interviewing any witnesses they could and narrowing in on Mars.

Investigators tracked Mars — a Navy veteran — to where he was living Veteran’s Administration Building, and in July of 2022, conducted an emotional two hour interview with the suspect.

He told investigators several accounts of the killing throughout and at other times denied any involvement, the release said.

At one point, he told the officers, “She hurt me more than I ever hurt her,” Gulluni recounted, but when prompted further said he didn’t know what he meant.

“The defendant then, in a wrenching moment, without prompting from the investigators, acted out the crime,” Gulluni said. “He stood up, hunched over and made a striking motion downward four times with his left arm and then admitted that he hit Betty Lou with a rock. He sat down again and became very emotional, sobbing loudly.”

Gulluni chose not to speak on any evidence of sexual assault Thursday.

The evidence collected led investigators to charge Mars in 2022.

Mars was reportedly in visibly poor health during the Wednesday sentencing, Gulluni said, and “his next steps are only known to him.”

“While neither solving this case nor any punishment of the perpetrator will give Betty Lou a chance to live the life that she deserved, I hope today represents a significant step for her family in their mourning and how they are able to memorialize her, so many years later,” Gulluni said.

Betty Lou Zukowski was 10 years old when she was killed and dumped in the Westfield River on May 26, 1966. (Photo courtesy Hampden DA)