Whatcom County Sheriff Bill Elfo said the baby's father is in custody in connection with the case, but revealed few other details during a news conference Sunday evening that was carried live on KIROTV.com. Complete Sheriff's News Conference

SLIDESHOW: Investigators Scour 2 Scenes

The father, 42-year-old Jonathan V. Frazier, said he put the boy to bed Thursday night and awoke Friday to find him missing.

Investigators said the story didn't made sense.

"I think it's safe to assume it involves criminal activity, and that's why it was investigated. Any plausible or reasonable satisfactory answer for the child's disappearance was not apparent," Elfo said.

For three days, hundreds of searchers looked for the baby.

Investigators would not say who told them the baby's body was hidden, but they said Frazier is cooperating with the investigation and answering questions.

The baby's mother was never questioned about the case because she checked in to serve a prison sentence for robbery the day before Cecil was reported missing.

Relatives called both great parents.

"I've seen them interact with him. Both parents did a great job with baby Cecil. They really did," said Don Kleindel, a relative of the family.

Relatives said the baby's father had lots of family support.

"He had plenty of help to raise little Baby Cecil. In fact, the grandparents had already been talking about which days and so forth to watch the baby and very supportive of Vince in raising the child by himself," said Kleindel.

A spokesperson for the baby's family said Monday, "We continue to rely on God’s strength and His grace to help us during this time of sorrow. Our faith remains strong even with so many unanswered questions. We will put our love and support into the family as we make arrangements for the funeral and the grieving period that will follow. Thank you for all your prayers and support."

The medical examiner may release the cause of death Monday.