Documentary produced by Florida sheriff's office generates new lead for 1984 cold case of missing 8-year-old girl

A documentary produced by a Florida sheriff's office has generated leads for a 35-year-old cold case of the disappearance of an 8-year-old girl who vanished after a trip to the corner store.

Marjorie "Christy" Luna had just gotten home from a Memorial Day weekend road trip with her family on May 27, 1984, when she left her home in Greenacres, some 10 miles southwest of West Palm Beach, to go to the store, according to a documentary created by the Palm Beach County Sheriff's Office titled "The Lead: Finding Christy Luna."

Luna informed her mother, Jennie Johnson, that she would be going to Greenacres Grocery, just two blocks and 400 feet from her home, to pick up some cat food for the family's newborn kittens, Boo Boo and Skeeter. She left around 3 p.m. that day and never returned, authorities said.

It is unclear whether Christy went directly to the store, which is within view of the corner of Christy's home, or if she stopped by a friend's house on the way, Palm Beach County Sheriff's Det. William Springer said in the documentary. She also could have stayed at the store until about 6 p.m. to play arcade games or gone to the neighborhood park frequented by local children, Springer said, adding that she was barefoot and in a turquoise jumpsuit at the time.

A cashier at the store remembered selling cat food to Christy between 2:30 and 3 p.m, according to the documentary. Police were called around 10:15 p.m. after Christy's mother called a few of her friends and knocked on neighbor's doors, Springer said.

It was a time before cable television, cell phones and computers, when kids would ride their bike around the block unsupervised, the detective said.

Several persons of interest had been investigated in Christy's disappearance, including a pair of brothers who lived in the neighborhood who had been convicted of molesting Christy's 6-year-old friend, a New Hampshire man, whose parents lived nearby, who was suspected in the disappearance of another 8-year-old girl in the Northeast, and another neighbor whose home Christy may have passed while walking to the store. The case was never solved.

The documentary, released earlier this year, generated "probably one of the best and most credible leads" investigators have received to date, Palm Beach County Sheriff Ric Bradshaw told reporters in a news conference Monday morning.

The sheriff's office has partnered with anthropologists from Florida Gulf Coast University for an excavation at a site near where Christy was last seen, Bradshaw said, apparently to dig for her remains.

"We believe that that this is another dot connecting all the dots to hopefully solve this case and bring some closure here," Bradshaw said.

The documentary appears to have worked as investigators intended.

"This, I'm hoping, goes out nationwide, and maybe somebody might remember something that stood out in their mind back then," such as a neighbor who "up and moved right away" or changed their car or their appearance, Springer said in the video.

In the documentary, Johnson described her daughter as a "ray of sunshine" whom "everybody loved."

"She was so sweet," she said.

Johnson, who moved back into the home where she lived when Christy disappeared in 1984 in case she needed to find her, ended Monday's press conference hopeful that they would discover what happened to her daughter.

"It has been 35 years, two months and nine days today, she said. "I think we're gonna bring Christy home."

ABC News' Ben Stein contributed to this report.