Sisters fight to keep their mother's killer behind bars as he comes up for ...

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More than two decades after their mother' body was fished out of a river inside a duffel bag weighed down with concrete, two California sisters are leading the charge to keep her convicted killer - their stepfather - behind bars for the rest of his life.

Tippy Dhaliwal was 14 years old and her sister, Jeanette Marine, was 10 when their mother, 33-year-old Phonthip Ott, went missing from their home in Sacramento in May 1992.

After a weeklong search, a fisherman pulled a large white nylon bag from the Sacramento River, which contained the missing mother's lifeless body.

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Rocky marriage: US Coast Guard Chief Petty Officer Dennis Ott, is pictured with his bride, Phonthip Boonack, right, on their wedding day, long before her murder and his arrest  

Rocky marriage: US Coast Guard Chief Petty Officer Dennis Ott, is pictured with his bride, Phonthip Boonack, right, on their day, long before her murder and his arrest  

Sisters' battle: Phonthip's grown daughters, Jeanette Marine (left) and Tippy Dhaliwal (right), are now fighting to keep their stepfather from getting out of prison on parole 

Sisters' battle: Phonthip's grown daughters, Jeanette Marine (left) and Tippy Dhaliwal (right), are now fighting to keep their stepfather from getting out of prison on parole 

Investigators quickly zeroed in on Phonthip's husband, Dennis Ott, as the prime suspect, and in 1995 he was found guilty of murder and sentenced to 25 years to life in prison with the possibility of parole, according to a recent CBS' 48 Hours episode dedicated to the crime. 

Phonthip's daughters have attended every one of Ott's parole hearings over the last 20 years, most recently in September 2015, each time voicing their vehement opposition to his release.

‘Why can’t he just sit there and rot?’ Tippy Dhaliwal said of Dennis Ott. ‘Where are the rights of our mom? She doesn’t have any rights.’

Her sister added that it’s frustrating that 25 years after their mother’s violent death, they are being forced to relive their childhood trauma and hear the grisly details of their mother’s murder every time her convicted killer comes up for parole.

‘We’re still being victimized and he’s behind bars,’ said Jeanette Marine.

Dennis Ott was arrested two years after his wife's body was found in the Sacramento River

Ott is seen in his mugshot

Ott, pictured in his mugshot, was arrested two years after his wife's body was found in the Sacramento River 

Phonthip Boonack was an immigrant from Thailand and a single mother-of-two; her daughters remembered her as a fun mom 

Phonthip Boonack was an immigrant from Thailand and a single mother-of-two; her daughters remembered her as a fun mom 

Ott, a former US Coast Guard Chief Petty Officer who is now in his 60s, has always maintained his innocence.

Speaking to CBS reporter Tracy Smith by phone from the Solano Prison in California, the inmate argued that he deserves to be freed because he meets all the criteria to be released on parole, and during his incarceration he has been a model prisoner, even earning a couple of college degrees.

‘I don’t believe I’ll be a danger to society,’ he insisted.

But Sutter County District Attorney Amanda Hopper, who represented Tippy and Jeanette at latest Ott’s parole hearing, is of a markedly different opinion.

‘I absolutely think he is a danger to society in general and probably to the family,’ Hopper said. ‘I’ve seen that he has absolutely no concept of accountability.’

US Coast Guard seaman Dennis Ott was 41 years old when he met Phonthip Boonack, an immigrant from Thailand and a single mother-of-two, at the home her stepfather, retired military man Larry Lewis.

The couple soon got married, but Tippy, Phonthip’s oldest, was distrustful of her new stepfather from the outset.

Both sisters said their mother's marriage to Ott was punctuated by fights and screaming matches, which became more frequent and intense leading up to her disappearance.

During Ott’s murder trial, 13-year-old Jeanette would tearfully recount for the jury how she once witnessed her stepfather put his hands on her mother’s neck during one heated argument.

This fisherman reeled in a white nylon duffel bag containing Phonthip's lifeless body following a week-long search

This fisherman reeled in a white nylon duffel bag containing Phonthip's lifeless body following a week-long search

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