CAMBRIDGE, MINN. – The mystery surrounding a Maple Grove girl missing since 1989 deepened Tuesday as local, state and FBI investigators dug up rural property owned by Amy Sue Pagnac's parents.

After searching the family's Maple Grove house and back yard just over a week ago, authorities continued to ramp up work on the 25-year-old cold case, with five forensic scientists and more than a dozen investigators excavating the family's wooded Isanti County property.

Police said Tuesday they plan to be there 24 hours a day through at least Friday, searching for any clues in the 1989 disappearance of the 13-year-old.

"Every day that goes by, we're closer to finding Amy," Maple Grove police Capt. Keith Terlinden said. "This is important to us, and this is important to the Maple Grove community."

More than 50 miles north of the suburb, the wooded dirt maintenance road that leads to the 140-acre Pagnac property was blocked Tuesday by yellow police tape as more than a dozen law enforcement vehicles, including a Maple Grove dump truck, were parked nearby. Terlinden declined to say why authorities are searching the property, what they're looking for or whether they've found anything on the land, about 9 miles outside of Cambridge.

No suspects have been named in Pagnac's case.

"It's a process, and the process will be complete when Amy is found," he said.

While the growing attention on her daughter's case is comforting to Susan Pagnac, she reiterated Tuesday that she believes Amy, who would turn 38 on June 15, was abducted and is alive.

"I just need them to stop fixating on the concept that she's dead and start looking for her," she said Tuesday from the family's Maple Grove home, where she and her husband put back items that police had boxed up after last month's six-day search. "I'm sorry. It's just very frustrating to me that everyone assumes my daughter is dead."

On Aug. 5, 1989, Marshall Midden, Susan Pagnac's husband, told police that he and Amy went to tend crops at the family's farm about noon and were returning about 5 p.m. when he stopped at an Osseo gas station 2 miles from their home. He told police he used the bathroom, came outside to find the car empty and assumed Amy was in the women's bathroom. But, he said, she had vanished.

Farming the land

Now, nearly 25 years later, the cold case is resurfacing after police got a sealed search warrant May 18 for the family's home, spending six days examining items inside and digging up the back yard and a concrete patio.

On Tuesday, Pagnac said police didn't tell her they were searching their farmland now, but she said she thinks the search — like last month's search — is to rule out steps in the investigative process.

"I assume they're just going through the paces that they did back then," she said. "I don't really care as long as they do what they need to do."

In 1987, the family bought the property, in the 37000 block of Verdin Street NW., in Maple Ridge Township. Pagnac said they used to bring Amy and her younger sister, Susan Jr., to hunt mushrooms or play on a tire swing as she and Midden farmed vegetables or harvested trees. Two of the family dogs are buried there, she said.

The property has a barn and an old trailer but no house; the couple plan eventually to build one and retire there.

Pagnac said police searched the land in 1990, but she doesn't know why or whether anything was found. While the family still visits the land, she said the farming stopped in 1993.

'Our goal is just to find Amy'

Maple Grove police, though, declined to confirm whether investigators have searched the property before.

On Monday starting at 9 a.m., they began their work, with a sealed search warrant. They're partnering with the FBI, the state Bureau of Criminal Apprehension and the Isanti County Sheriff's Office.

Despite the excavating, Terlinden said investigators think Amy could be dead or alive.

"Our goal is just to find Amy," he said.

Less than a mile away from the Pagnac farmland, Allen DeJoode watched as law enforcement vehicles concentrated near the property and a TV news helicopter flew overhead. He's lived on neighboring land for more than 50 years and said that, since Pagnac and her family bought the former tree farm, they have kept to themselves.

Another neighbor, Steve Erickson, said federal and state law enforcement were on the property four or five years ago, but he didn't know what they were doing then.

"It's all very interesting," he said. "I don't have a clue what's going on. But I can't believe it."

Staff writer Paul Walsh contributed to this report. Kelly Smith • 612-673-4141

Twitter: @kellystrib