Kristi Richardson's tidy home was undisturbed when police arrived on Oct. 7 -- the front door deadbolted, both cars in the garage and the recently-widowed trucking executive's purse where she always left it. But there was no sign of the 61-year-old grandmother that day or since, and her disappearance has left loved ones and law enforcement in Casper, Wyo., stumped.
Her family is convinced Richardson met with foul play, but police say there's not enough evidence yet to classify her disappearance a crime.
"The hard part of this case is that she is literally the only thing missing from her home," Capt. Steve Freel of the Casper Police Department told FoxNews.com. "This is truly going back to 1950s police work."
Richardson, the longtime owner of a trucking business in Casper, was last seen on Oct. 6 when she drove to her daughter's home -- on the same block -- to drop off a birthday card and visit her grandchildren. Phone records show that later that day, at 7:45 p.m., Richardson took a routine phone call from one of her drivers. The next call to Richardson's phone, at 11 p.m. and from a vendor that does business with Richardson Trucking, went unanswered.
When Richardson did not show up for work the next morning, her 41-year-old daughter, Amber Fazio, entered her home using a spare garage door opener. No one was home, and the house was undisturbed, according to Fazio. In addition to the purse, which held Richardson's ID and $800 cash, Fazio told FoxNews.com her mother's cellphone was in the home.
"Nothing was disturbed," Fazio recalled the morning she entered the home searching for her mother. "Her front door is a dead bolt so that’s the only way you can unlock it. Quite a few sliding glass doors within the house were all locked. There was no sign at all of forced entry."
Freel said he is looking at several possibilities, including that Richardson might have been targeted by a current or former employee of Richardson Trucking, a well-known trucking company she owned with her late husband since 1979. Freel said detectives are also investigating employees at competing companies in the investigation, noting that a booming oil and gas industry has brought an influx of people and new businesses to the area. But he still can't say that a crime has even been committed.
"Do we suspect foul play? Absolutely, but we're also keeping an open mind," Freel said. "Was there somebody else she left with? Was she taken against her will? We’re looking across the board at all the possibilities."
Crime is low in the central Wyoming city of 55,000. But Freel noted that the burgeoning local oil and gas industry has brought a host of strangers to the state's second-largest city.
"Wyoming right now is booming," Freel said. "The crime rate in Casper is not high but we've seen quite an increase over the last six months."
"It's become a lot higher and a lot more violent," he added, noting the city has had seven stabbings or shootings over the past six months.
Richardson's family, meanwhile, is offering a $25,000 reward for any information leading to her whereabouts. Fazio is convinced her mother and grandmother of five is the victim of foul play.
"I think that someone has her or had her," Fazio told FoxNews.com. "I don’t think that she did this on her own."
"She never left the house without using her car," she said. "My gut tells me that someone was there before she got home."
Richardson's husband died in 2013. Fazio said that when her father once suggested retiring from the business and moving to Arizona, her mother remained committed to running the company they had founded 35 years ago.
"She's very strong-willed in running that trucking company," Fazio added. "It was her life."
Cristina Corbin is a Fox News reporter based in New York. Follow her on Twitter @CristinaCorbin.