Kansas City, Mo. ? The FBI has opened an investigation into the disappearance of two Independence children who have not been seen since they were taken by their father in 2004, an FBI spokesman said.

Sam and Lindsey Porter were 7 and 8 years old when their father, Dan Porter, picked them up from his estranged wife on June 5, 2004, for a weekend visit. The children’s whereabouts remain a mystery, and Dan Porter has told several different stories about what happened to them.

The children’s mother, Tina Porter, who has criticized police handling of the case, was pleased when told the Independence Police Department had asked for FBI assistance.

“I think somebody else’s eyes looking into the case could find something that the police department overlooked,” she said.

Daniel Porter was convicted in February of parental kidnapping with the intent to terrorize his ex-wife and was sentenced to 38 years in prison.

FBI spokesman Jeff Lanza said the bureau had offered to help when the children disappeared but police turned down the offer.

“But I don’t think it was a case where the police said, ‘We’re not going to ask the FBI to participate,'” he said. “I think if they had something for us at that time to do, they would have asked us to do it.”

The FBI did have an expert on personality traits examine Daniel Porter’s interrogation tapes and created age-enhanced images of the children. But that was the agency’s only involvement.

“We’ve periodically, throughout the investigation, talked to the FBI,” said David Lamken, deputy chief of the Independence Police Department. “And Tina did raise the issue that she thought the FBI should be more involved. We’re trying to do everything we can to help Tina and make sure we covered all the bases.”

Lanza said an FBI agent would go over the case file and help police determine whether more could be done.