Detectives believe woman who claimed to be missing 13-year-old Mary Day and had DNA match was an impostor and the girl was murdered by her stepfather who was 'possessed by demons' on the night she disappeared

• New details have emerged about the bizarre case of Mary Day who vanished around 40 years ago in Seaside, California
• The 13-year-old girl disappeared in 1981 but was not reported missing by parents
• Her sister reported her missing in 1994 and a case opened in 2002
• Detectives believed her stepfather William Houle murdered her
• As police built their case a woman turned up in Arizona claiming to be Mary 
• DNA proved she was the mother's daughter
• Detectives told CBS '48 Hours' they are skeptical she was the 'real Mary Day' 
• In a clip released Friday, Mary's sister Sherri Calgaro said her mother would often talk about hiding bodies in California
• 'William told me that he didn't kill Mary but that his wife told him he was possessed that night and that he had a demon inside of him,' a detective said

Detectives believe a woman who claimed to be a missing girl two decades after her disappearance may have been an impostor and the 13-year-old was actually murdered by her stepfather who believed he was possessed by demons back in 1981. 

New details have emerged about the bizarre case of Mary Day who vanished around 40 years ago in Seaside, California.

The little girl disappeared in 1981 but was not reported missing for over a decade with her parents telling her two sisters she had ran away from home. 

More than two decades later and as the net appeared to be closing in on the parents, a woman claiming to be the missing girl appeared and DNA proved she was her mother's daughter. 

New details have emerged about the bizarre case of Mary Day (pictured) who vanished around 40 years ago in Seaside, California

But detectives remain skeptical that the woman - who is now dead - is the real Mary Day as theories continue to circulate that she was murdered decades ago, according to a CBS '48 Hours' episode called 'What Ever Happened to Mary Day?' airing on Saturday.     

In a clip released Friday, Mary's sister Sherri Calgaro, who was 10 at the time of her disappearance, told CBS she had been convinced as a child that her sister had been murdered.  

She said her mother would often talk about hiding bodies in California.

'My mother told me there were many places in California you could bury a body and it would never be found,' she said.

'I started believing she was murdered.'

Calgaro added that she and her sister Kathy were afraid to talk about their sister when they were growing up.

Mary's sister Sherri Calgaro told CBS '48 Hours' she had been convinced as a child that her sister had been murdered and her mother would often talk about hiding bodies in California

Seaside Police Chief Steve Cercone also told CBS he had his doubts about the identity of the woman who reappeared years later - nicknamed 'Phoenix Mary'

'I lay in bed one night with Kathy and I asked her what happened with Mary and she was like "shhh don’t say anything, we're not allowed to talk about Mary,"' she said.  

Seaside Police Detective Joe Bertaina told CBS he thought the girl had been murdered after he interviewed Mary's stepfather William Houle. 

'William told me that he didn't kill Mary but that his wife told him he was possessed that night and that he had a demon inside of him,' he said. 

The little girl had been taken into protective custody the year before her disappearance because her stepfather had reportedly been physically abusing her. 

She had only returned to live with the family a few months before she vanished.

Mary and her stepfather William Houle. A detective said: 'William told me that he didn't kill Mary but that his wife told him he was possessed that night and that he had a demon inside of him'

Seaside Police Chief Steve Cercone also told CBS he had his doubts about the identity of the woman who reappeared years later - nicknamed 'Phoenix Mary'.

He said he had ‘never seen a case like this’ where a little girl ‘disappeared off the face of the earth’ and her parents did not report her disappearance. 

He recounted the moment a colleague called him and told him Mary Day had been found 22 years after she disappeared.  

'He told me, "Hey captain are you sitting down?" He says "Got to let you know that… they say they found Mary Day,"' Cercone said. 

Cercone told CBS he thought the woman may be an 'impostor' but the woman was ‘adamant she was the real Mary Day’.

Phoenix Mary's ID: More than two decades later and as the net appeared to be closing in on the parents, a woman claiming to be the missing girl appeared

Some detectives now believe Phoenix Mary - who died in 2017 - was the 'real Mary'.

In 2017, acting chief of the Seaside Police Department Judy Veloz visited her.

She told CBS, Mary directed her to Morie Kimmel - a woman who took her in after she ran away. 

A photo taken a year after the 13-year-old disappeared showed Kimmel and a girl that looked like Mary.   

Calgaro told CBS she also now believes the woman is her missing sister after she traveled with '48 Hours' to visit her shortly before her death. 

THE MYSTERY OF MARY DAY

The mystery began when 13-year-old Mary Day vanished one day back in 1981. 

William admitted to police years later that he had beaten the girl the night before her disappearance. 

Her parents, Charlotte Houle and stepfather William Houle, did not report her missing and as the family moved around a lot because William was in the army, no-one other than her sisters noticed her disappearance. 

In 1994, as an adult, Mary's sister Sherri Calgaro, who was 10 at the time of her disappearance, filed a missing persons report for her sister. 

Seaside Police launched an investigation in 2002, led by Seaside Police Detective Joe Bertaina. 

In 2003, he took Mary's other sister Kathy back to the family home in Seaside and she showed him an area of the yard where she said her parents told her not to play.

Cadaver dogs - which locate human remains - alerted officers to the same area. 

A body was not discovered but a little girl's shoe was found.  

Charlotte and William Houle were interviewed by police and told officers Mary had run away. 

'She started running away,' Charlotte is heard saying in the police tape.

When police asked the mother why she was not concerned with finding her daughter she said: 'If she's dead, she's dead.'

William also admitted to fighting with Mary. 

Police suspected Mary had been murdered by William and Charlotte helped cover it up.

Just nine months after the parents' interviews and as the case was being built against William, a woman claiming to be Mary turned up in Phoenix, Arizona, when police pulled her over for a routine traffic stop.  

But suspicions surfaced when officers discovered her ID had been issued only three weeks earlier and just months after Charlotte and William were interviewed by police.

DNA tests then proved the woman was Charlotte's daughter.  

But police and Mary's sisters still had doubts because the woman had a thick southern accent, did not know about the inheritance from her father, and did not know many details about her childhood.

The woman's mail was also found addressed to a woman named Monica Devereaux. 

Mary with her sisters Kathy and Sherri before she disappeared