Christine Hill only got to spend 10 years of her life with her mother. â€śThatâ€™s all I had with her. Ten years,â€ť Christine told Dateline. â€śAnd I thank God for every one of them.â€ťChristine was only 10 years old when her mother disappeared in 1981. Christine, her 8-year-old brother, their mother, Diana Lynn Harris, all moved down to the Florida Keys from Michigan with Dianaâ€™s boyfriend earlier that year for a new start.â€śShe lost her job in Michigan, so just decided to take a risk and move to Florida,â€ť Christine said. â€śShe planned on making a life down there for all of us.â€ť Diana landed two jobs: at the No Name Pub and at the Sugarloaf Lodge. Christine told Dateline that her motherâ€™s boyfriend didnâ€™t stick around for long, and Diana soon began dating another man named Gary Argenzio. Christine said she remembers happily exchanging their cold days in Michigan for the warm beaches of Florida – specifically Big Pine Key where they settled. It was paradise.But after three months in paradise, Christine and her brother were sent back to Michigan to spend the summer with their father and other relatives. They said goodbye to their mother at the airport in Miami on June 7, 1981. â€śIt was the last time I ever saw her,â€ť Christine said. She added that the last time she spoke to her mother was on July 15 when they talked on the phone. â€śShe called us regularly,â€ť Christine said. â€śSo when she stopped calling, and when we couldnâ€™t get in touch with her, we knew something was wrong.â€ť Diana was scheduled to pick the children up in Michigan on August 15 so they could then go attend her sisterâ€™s wedding in Illinois. She never made it. Let our news meet your inbox. The news and stories that matters, delivered weekday mornings.Christineâ€™s grandmother filed a missing persons report in Monroe County, Florida. But 39 years later, Diana still has not been found. After their motherâ€™s disappearance, Christine and her brother stayed in Michigan and were raised by their grandmother. When Christine turned 17, she returned to Florida for a short time to begin her own investigation. Sheâ€™s been at it ever since. â€śSome information Iâ€™ve come across leads me to believe that my mother may have become a threat to a major drug operation at a party house on Big Pine Key where my mom lived,â€ť Christine said. She added that after they were sent back to Michigan, her mother and Gary Argenzio moved into a house on Tortuga Lane in Big Pine Key known by locals as the â€śparty house.â€ť The house was owned by one of Argenzioâ€™s friends, who was also a local attorney. Christine said she later learned that Diana had called a friend in Michigan and said she feared there was going to be a drug bust at the party house. It is unknown when this call took place. For years, Dianaâ€™s case went cold. It wasnâ€™t until 1995, at Christineâ€™s urging, that Dianaâ€™s case was brought back into the light. Detective Sergeant Barney Sajdak with the Monroe County Sheriffâ€™s Office told Dateline that their records on Dianaâ€™s case only date back to 1995. He said that the reports note that Diana was reported missing in 1981, but that there was no official report.He confirmed that Dianaâ€™s case was re-investigated in 1995 as a possible homicide and that many people were interviewed, including Dianaâ€™s boyfriend, Gary Argenzio, but no one was arrested in her disappearance. Detective Sergeant Sajdak told Dateline that the report included police interviews with two men who knew Argenzio. They told detectives they believed Argenzio murdered Diana and dumped her body in the ocean. Shortly after Dianaâ€™s disappearance, Gary Argenzio stole a boat and fled to Mexico where he stayed until he was arrested in 1982 for theft, according to Det. Sgt. Sajdak. He was sentenced to five years in prison. In 1992, Argenzio died at his home in Florida, according to a medical examinerâ€™s report in Dianaâ€™s file.â€śItâ€™s a tough case,â€ť Det. Sgt. Sajdak told Dateline. â€śDecades have passed, the detectives who worked on the case are gone, some of the witnesses are gone. Itâ€™s hard to say if we will ever find her.â€ť Diana Lynn HarrisHe added that the investigation into Dianaâ€™s disappearance is ongoing and he urges anyone who may have information to call the sheriffâ€™s office.â€śA piece of information that may seem insignificant could be the piece to solve this case,â€ť Det. Sgt. Sajdak said. â€śIf you know something, please call us.â€ť Now, nearly four decades later, Dianaâ€™s daughter still fondly remembers the 10 years she spent with her mother. â€śI think of all the places she took us for fun, the times she did my hair for school and when she cooked breakfast for us each morning. She really was such an amazing mom who gave my brother and I lots of love and affection,â€ť Christine told Dateline. â€śShe was active in every part of our short time with her. I had my first 10 years of life with her, some people don’t get that. And so I am thankful to God for every bit of time we had. We were very blessed.â€ťChristine added that she remembers her mother being a â€śwonderful motherâ€ť even though she led a difficult life. She felt like their move was an escape for her mother, but unfortunately led to the end of their time together. â€śI have beautiful memories of my life with her. She worked hard, cooked wonderful food, and was never too busy to play with my brother and me,â€ť Christine said. â€śNo matter how tired she was or how weighed down by worries, she gave us unstinting love and attention.â€ťThroughout the years, Christine has put together files of information that she hopes will one day lead to answers in her motherâ€™s case. Although 39 years have passed, Christine tells Dateline she isnâ€™t giving up. â€śFor 39 years now, Iâ€™ve been trying to find out what happened to her, and I will not stop until I get an answer.â€ťAnyone with information about Dianaâ€™s case is urged to call the Monroe County Sheriff’s Office – Special Investigations Division at (305) 289-2410.