MILFORD - The family of 4-year-old Jonathan Loja, who was killed by a hit-and-run driver on Easter, is happy a suspect was arrested Thursday. But they are upset the driver didn't come forward at the time of the accident.

Police arrested Milford resident Melissa Knight, 54, of 88 Depot St., at 2:30 p.m. Thursday in Newton. She is charged with leaving the scene of a motor vehicle crash after causing injuries that resulted in a death, and misleading a police investigation.

Police say Knight actively attempted to cover up her involvement in the accident, and that DNA is a key piece of evidence that led to her arrest.

She’s being held on $100,000 bail at the Milford Police headquarters ahead of her arraignment Friday in Milford District Court.

"I feel justice has been served," Jonathan's aunt, Maria Guaman, said Thursday during an interview in her Milford home.

When Jonathan, who lived in Framingham, was found by a family friend lying in the street gravely injured, everyone was shocked that he had been hit by a car, said Ana, Jonathan's 12-year-old cousin, who asked that her last name be withheld.

"I feel upset that she didn't come forward initially," Ana said.

Knight’s arrest marks a major break in the hit-and-run death on Water Street, just a few blocks from where Knight lives. Jonathan was hit after he ran into the street chasing a toy. Early on, police narrowed their focus to three vehicles believed to be involved and asked the public to help find them.

Jonathan's mother, who was in Milford at a family Easter party, heard a popping sound around the time of the crash, Ana said. But she did not realize her son had been hit by a car.

According to police, Knight was arrested at Lasell College in Newton. According to a LinkedIn profile, Knight works at the school as the coordinator of intergenerational programming.

According to an arrest warrant affidavit, Knight voluntarily went to the police station on April 19 - three days after the crash - to talk to detectives about the crash. She brought her gray 2009 Chevy Traverse to the station.

According to Police Chief Tom O’Loughlin, Knight said she realized police were looking for a Chevy Traverse that they believed was involved in the crash. Knight, who drives a Traverse, brought it to police in an attempt to clear her name.

“A check of her vehicle … revealed that the vehicle was extremely clean while most cars were covered in pollen and rain spots,” police wrote in the affidavit.

Knight said she hadn’t washed the SUV in over a week, but police say Knight brought her Traverse to a professional car wash in Milford the morning after the crash.

Also, a small piece of plastic recovered from the crash scene matched a missing broken piece of trim from Knight’s vehicle.

Knight told police a dent on the front of her SUV was from a tree limb falling on it over the winter, but the investigation revealed otherwise and her attempted cover-up didn’t stop there, police said.

“There are signs of tampering on the hood and front end of the vehicle indicating that someone had attempted to remove the damage to conceal the vehicle’s involvement in the crime,” the affidavit says.

Investigators found blood spots on the undercarriage of Knight’s vehicle. Police said the DNA from those blood spots matched DNA in a sample of Jonathan's blood.

The affidavit quotes witnesses who said Knight stopped her SUV after the crash and then drove away.

At Milford police headquarters, Chief O’Loughlin offered few other details about the case. Any additional charges are up to the Worcester district attorney's office, he said.

Knight’s vehicle was on a list of Chevy Traverses that investigators wanted to check, but she brought it to the station before police had an opportunity to reach out to her, O'Loughlin said. That was after police say she had it cleaned and attempted to fix the dent.

Another Traverse with front-end damage was brought to the station, but police determined its damage was from an unrelated collision.

“Great work done by detectives,” Chief O’Loughlin said. “They’ve been working 18 hours a day, plugging away each and every day.”

A neighbor was unable to confirm who Knight lives with, but said they don’t speak often. A knock on Knight’s door went unanswered. Her Facebook account was deactivated just hours after her arrest.

Loja’s family was notified that the person who allegedly killed their son was arrested, Chief O’Loughlin said.

“They’re just grateful for the effort and work detectives have done,” he said. “Nevertheless, the tragedy is theirs. They lost their son.”

Daily New Staff reporter Christian Yapor interviewed Maria Guaman, who speaks only Spanish, and translated her comments into English.

Zachary Comeau can be reached at (508) 634-7556 and zcomeau@wickedlocal.com. Follow him on Twitter @ZComeau_MDN.