Police are not certain whether the victims were killed elsewhere and dumped on the property -- or even when.
"It takes a very certain profile of an individual to kill a child," says Ebert, who declined to elaborate on consultation with the FBI's behavioral analysis unit.
"We either haven't reached the family members we need to, or we missing their family members and for their own reasons they are not coming forward."
One day, grave marker may bear names
Ronda Randall and her brother, maintain a blog about the Allenstown case and have provided some information they've gleaned to police.
"This case is so compelling," says Randall, who grew up in southern New Hampshire and now lives in Maine. "This story has been very quiet."
The siblings, who on their website say they do not represent a law enforcement agency, have talked with hundreds of people. Ebert says the pair have been in contact with state police.
Randall praises police for their doggedness and said she believes the case will be solved.
She believes she and her brother are in a sense a proxy family for the victims.
A grave marker at a church cemetery in Allenstown -- a town of about 4,400 east of Concord -- refers only to the first two victims found.
"May their souls find peace in God's loving care," the inscription reads.
One day, Randall says, she would like the grave marker bear names of the four victims. "I want to see it resolved."
Social media might have made a difference
The woman and the girls were killed before there was text messaging, Facebook and other forms of social media -- a fact not lost on investigators.
And, back in 1985, police did not have a clearinghouse for missing people. The National Center for Missing and Exploited Children had been in existence for only one year.
Social media is a valuable tool for investigators, says the center's Williamson, who leads a five-member team.
"From the missing side it has helped in a lot of cases," she says. "You can see who perhaps who they were talking to. With teenagers, their friends know more than their families know."
Unlike in 1978 or 1985, people nowadays are extremely connected, be it through cell phones, e-mail or social media.
"If you don't get a text within two hours you might wonder what is going on," says Williamson.
Still, she cautions, there are still cases today when people "are not reported missing for various reasons."
Ebert says someone critical to identifying the four victims may not have come forward because of a sense of criminal liability or guilt for not having provided clues sooner. The victims, he says, may have been part of a disjointed family.
He hopes the DNA testing may clearly show the relationships among the four victims, providing police and the public more opportunities to identify them. "It's an awful tragedy to lose a person to a homicide. It is terrible miscarriage of justice not to know who carried out the crime against your loved one."
Williamson and her team are working on 650 cases involving unidentified children. The oldest case is from Arizona, in 1933.
Since November 2011, the team has helped identify seven children, one of whom was a victim of Gary Ridgway, the so-called Green River Killer, she says.
DNA helped solve the cases. Now Williamson hopes to give a family a sense of closure.