"Adam's gone and his mother's gone, and those are the two people that could give us the most information to the questions that all of us have," he said.
The Parkers, who have two other daughters, ages 3 and 5, said they're not angry because they know they can't undo what happened at the school that day.
"So the idea of wasting any energy on anger towards somebody or trying to point blame at anybody seems like a waste of time and energy that we can use to be better parents to our girls," Robbie Parker said.
Alissa Parker said she believes Nancy Lanza bears some accountability for what happened. The Bushmaster rifle used in the school shootings belonged to Nancy Lanza.
Asked whether she forgives Adam Lanza, Allisa Parker said it's not her burden to bear.
"I do hold him accountable, but I feel like God will determine that," she said. "And I feel like he's in a place where the judgment will happen, and I don't have to. I don't have to judge him, and I'm at peace with that."
Associated Press Writer John Christoffersen in New Haven, Conn., contributed to this report.