NORTHAMPTON — Almost a year to the day Florence teen Jesse Johansmeyer was killed after being struck by a pickup truck at a bonfire party in Hatfield, a suspect has been charged in his death.

Prosecutors are not naming the suspect because he is a juvenile, Northwestern district attorney’s office spokesperson Laurie Loisel said Thursday. He is set to be arraigned in Hadley Juvenile Court on charges of negligent motor vehicle homicide and leaving the scene of an accident causing personal injury, Loisel said.

Proceedings in juvenile court, which has jurisdiction over youths ages 12 to 18, are not open to the public, and Loisel said details of the suspect’s age, hometown and the arraignment could not be released.

Johansmeyer, 19, was at a bonfire in the Hatfield meadows near the Connecticut River when he was hit by a vehicle that drove away at around 11:30 p.m. last March 24, authorities have said. Others at the party called 911 and tried to help him, but he died at Baystate Medical Center early the next morning.

A 2022 graduate of Northampton High School, Johansmeyer was remembered by friends and classmates as warm and humorous, someone who liked sports and the outdoors and who put a smile on other people’s faces.

His mother, Darlene Thorpe, wrote in an email Thursday the family feels it has taken far too long for charges to be brought.

“Though it is a step forward, we have many more steps to take,” she wrote. “Grief is a lifelong process and one that is unpredictable, indescribable and different for each individual.”

First Assistant District Attorney Steve Gagne said investigators have been in contact with Johansmeyer’s family throughout.

“We truly appreciate their patience through what has been a long and frustrating process,” he said. “We hope the issuance of charges will represent one step closer to justice for them.”

Gagne said the police investigation, conducted by State Police assigned to the district attorney’s office and Hatfield police, was meticulous and thorough “from the get-go.”

There were many people to interview and forensic evidence to be tested, he said.

“We wanted to be sure we identified the correct suspect, and gathered any and all evidence,” he said.

He said the suspect is the person police and prosecutors “believe was driving the vehicle that struck and killed Jesse,” and he doesn’t anticipate that anyone else will be charged in the case.

If proved, the charges, which are misdemeanors, are likely to result in commitment to the Department of Youth Services rather than jail time.

“Juvenile court is not designed to be punitive — it’s designed to be rehabilitative,” Gagne said. He noted that the suspect has hired an attorney and has remained in the area since the incident.

To mark the one-year anniversary of Johansmeyer’s death, a vigil will be held Saturday from 7 to 8 p.m. at Childs Park.

“We will continue to find ways to share Jesse’s story, his memory, his life and to be vigilant in getting those who were responsible held accountable,” Thorpe wrote.

She and Johansmeyer’s sister, Willow Vandoloski, have developed a website, Jesse’s Justice, offering information on support for those grieving or experiencing trauma. The site offer links for parents and siblings, trauma and grief counseling resources, videos, and articles on grief and loss.

They say they have found it challenging to find assistance, especially local and consistent support.

Of the website, she wrote, “We published it two weekends ago so it would be done in time for the anniversary. It was a labor of love and so much more.”