The 1991 death of Kathy Page remains under investigation.
The reward has increased in the real-life case that inspired the Oscar-winning film Three Billboards Outside Ebbing, Missouri.
Officials in Texas, where Kathy Page was found strangled in 1991, are now offering $6,000 for information that helps crack the decades-old case.
Page was found dead in her car in what police determined was a staged scene made to look like an accident.
Page's father, James Fulton, has spent the years since putting signs up along I-10 in a bid to bring attention to his daughter's unsolved murder, signs like the one that says: "Vidor P.D. does not want to solve this case...The Attorney General should investigate."
Fulton believes the killing was carried out by his daughter's estranged husband. No charges have been filed against that man.
However, the Texas Department of Public Safety's announcement on Tuesday could give the 87-year-old hope that he'll finally get closure.
Twenty years ago, the billboards and Kathy Page's murder caught the attention of British writer and director Martin McDonagh as he was traveling through Texas on a Greyhound bus.
The film he'd go on to write and direct won Oscars for stars Frances McDormand and Sam Rockwell.
Fulton said he hasn't seen the film and that he didn't know it was nominated for seven Academy Awards but that he hopes it has brought his daughter's case more attention.
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