(CNN) -- The father of Haleigh Cummings, a Florida girl who disappeared in February, plans to file for divorce from the girl's stepmother, a key witness in the case, his attorneys told HLN's "Nancy Grace."



Ronald Cummings plans to divorce his wife, Misty, his attorney says.



The move follows weeks of reported tension between Ronald and Misty Cummings during the search for Haleigh, who was 5 when last seen.



In papers expected to be filed Tuesday, Ronald Cummings, 25, cites irreconcilable differences in ending his short marriage to his 17-year-old wife, said Terry Shoemaker, Ronald Cummings' attorney.



Haleigh went missing from her father's home in Satsuma, Florida, on February 9. Cummings has made several public pleas for information in her disappearance.



Misty Cummings, then known as Misty Croslin, was the last person known to have seen Haleigh the night she disappeared from the family's rented mobile home. The teenager said she tucked Haleigh and her 4-year-old brother into bed about 8 p.m. and went to sleep herself two hours later, but awoke at 3 a.m. to find the girl missing and a cinder block propping open a back door.



Ronald Cummings called police and reported his daughter missing when he returned from work at dawn.



Investigators have said they do not feel Misty Cummings has told them everything she knows.



"The police have been telling me that I've been keeping Misty under my wing and that's why she hasn't talked to the cops," Ronald Cummings told a "Nancy Grace" producer Tuesday. "So now, here you go, I divorced her. So now go find my baby."  Watch Ronald Cummings speak to Nancy Grace »



The Putnam County Sheriff's office said in August that "the evidence and investigatory effort has minimized the likelihood that Haleigh's disappearance is the work of a stranger." Ronald Cummings and Crystal Sheffield, Haleigh's mother, are not considered suspects, police said.



"Investigators believe that Misty Croslin-Cummings continues to hold important answers in the case," the sheriff's office said in a written statement. "She has failed to provide any sort of detailed accounting of the hours during the late evening and early morning of Haleigh's disappearance. Furthermore, physical evidence at the scene contradicts Misty's sketchy account of her evening activities." Shoemaker said his client told Misty Cummings he wanted a divorce on Sunday, and that the a divorce agreement was drawn up Monday. The agreement was sent to Misty Cummings' lawyer for her signature.



"He really didn't come to us and say, 'I want to file for divorce,'" said another of Ronald Cummings' attorneys, Brandon Beardsley. "My understanding is that this is something that he and Misty have been discussing for the last few days and they're contemplating it because they ultimately feel that it is in the best interest for both of them."



Misty Cummings' attorney, Robert Fields, told CNN he has not talked with his client and doesn't know her thoughts regarding the divorce. Fields said he had received the papers via e-mail but had not had a chance to review them. Asked what he thought the divorce would mean for the search for Haleigh, he said, "Probably nothing."



"You have to understand that ever since Haleigh went missing, they have been scrutinized," Beardsley said of the Cummingses. "They can't go out to dinner, can't even go to the convenience store to get a drink. ... The pressure of everything that is going on, the allegations and speculation, has been a stress on the relationship.



The two lived together for about six months before marrying in March. The divorce agreement provides no financial terms, according to Shoemaker.



On Monday, Misty Cummings left Satsuma to stay with a friend in Orlando, 50 miles south, Shoemaker said.
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