Reading from a statement on Tuesday, Desiree Young urged Terri Horman to "do the right thing" and cooperate with police, if for no other reason than for the boy's half-sister, toddler Kiara, "who loves him and misses him," reports Portland station KPTV.
Young and her husband, Medford police detective Tony Young, and the boy's father, Kaine Horman, said in an e-mail to news organizations late Monday that they still believe Terri Horman is withholding information.
Young also revealed that the day her son disappeared, Terri Horman was supposed to drive him to Eugene, Ore., where she was to turn him over to his mother and stepfather for a weekend in Medford. Tony Young said he planned to take Kyron on a long-delayed fishing trip with the rod his stepfather had given him for Christmas, KPTV reported.
Horman, 40, the last person known to see Kyron alive before he went missing, has taken two polygraph tests but has not been named a suspect or person of interest in Kyron's disappearance. However, the former elementary school teacher has hired a prominent defense attorney.
In addition, investigators have said a break in the case may be coming soon, after there emerged reports of an alleged murder-for-hire plot instigated by Terri Horman against Kaine Horman, her former husband and Kyron's biological father.