BARRON, Wis. — Cows and corn and silence stretch out on either side of Highway 8, beyond the Jennie-O turkey plant and 10 churches that serve this town of just over 3,400. So when James and Denise Closs, a quiet couple who had lived in town for decades, were found shot to death in their taupe house last month, residents were stunned. It was an agonizing loss of two lives, but also of a way of life.

Front doors are being locked. F.B.I. agents have descended. Yet after three weeks, residents are left with a terrifying mystery that goes beyond the shocking deaths: Not only have the authorities publicly identified no suspect, no murder weapon and no motive, but the Closses’ 13-year-old daughter, Jayme, has been missing ever since.

“We have a double murder and a missing 13-year-old girl, there’s not much more to tell than that — and that’s the frustration,” said Sheriff Chris Fitzgerald of Barron County, whose force of 78 ballooned at one point with 200 federal, state and local law officers joining an intensive, round-the-clock hunt.

[Jayme Closs has been found alive in Wisconsin. Read the latest. ]

More than 2,100 tips have turned up nothing. Law enforcement officials have turned a courtroom in a municipal building on the outskirts of town, about 90 miles northeast of the Twin Cities, into a nerve center for the investigation. Thousands of volunteer searchers have combed cornfields and cow pastures. And still nothing — no clues and no Jayme.