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Authorities have served a subpoena asking an Iowa-based NBC affiliate to turn over footage of its interviews with one of the mothers and grandmother of two missing cousins, saying they may contain clues about the girls' abduction.

Waterloo-based KWWL-TV announced Wednesday night that it received the subpoena seeking "raw video" of interviews conducted last week with Misty Morrissey and Wylma Cook, and made the document public on its website. The station's news director didn't immediately return a message Thursday seeking comment on whether it would comply.

The subpoena application, filed Monday by Black Hawk County Attorney Thomas Ferguson, says the footage is needed so his office can conduct a "complete investigation" into the disappearance of 10-year-old Lyric Cook and 8-year-old Elizabeth Collins.

The girls disappeared July 13 after taking a bike ride in Evansdale while their grandmother, Wylma Cook, was babysitting them. An extensive search involving local, state and federal investigators has failed to find them.

Authorities classified the case as abduction after a search by divers using sonar equipment ruled out the possibility their bodies might be recovered in an Evansdale near where their bikes were found. Investigators have focused attention on Lyric's parents, Daniel and Misty Morrissey, who have a long history of being involved in drugs, but have not called them suspects.

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The July 20 interview with Misty Morrissey being sought by authorities came days after the family said she had stopped cooperating with investigators or speaking to the news media, citing an attorney's advice.

During the interview, Morrissey told KWWL-TV reporter John Wilmer that she and her estranged husband sought legal advice after they were accused during lengthy interrogations of having involvement in the girls' disappearance. With her mother, Wylma Cook, standing next to her, she called it a "pretty intense coercion" and said the scrutiny was probably the result of her criminal record.

"They don't have anything else. We've been to a briefing last night. There's no other information, no new leads, no evidence, there's nothing," she said. "After seven days, I realize it's probably very frustrating for them that they probably haven't been able to come up with something. It's frustrating for us as well."

The subpoena application says the station "may have knowledge" of a crime that happened July 13.

"Without the production of documents from the person named, this Applicant feels that a complete matter of the investigation is not possible," Ferguson wrote.

KWWL -- whose letters stand for "Keep Watching Waterloo" -- has aggressively covered the case. Its veteran 10 p.m. anchor, Ron Steele, beat other reporters by an hour on July 20 by tweeting news that an FBI dive team had not found the girls' bodies in the lake. Its live interview earlier that day with Misty Morrissey also was seen as a scoop.