CRANDON, Wis. (AP) — The U.S. Fish and Wildlife Service is offering a $1,000 reward for information that leads to the arrest of someone who is poisoning pets and wildlife in northern Wisconsin.

Four dogs have died in the past month in Forest County. Testing on two of the pets, a 4-year-old yellow Labrador retriever that died April 24 and a 3-year-old German shepherd that died April 1, confirmed that they died from poisoning. Tests are pending after two more dogs died last weekend.

Officials believe the deaths are related to the ongoing poisonings in Florence, Forest and Marinette counties that have been investigated for about a year, WLUK-TV reported. So far, seven pet dogs have died.

Investigators also found dead coyotes, weasels and wolves, and lab tests confirmed the animals were also poisoned, WSAW-TV reported.

The dog deaths have all occurred on public land, investigators said.

The reward is for information that leads to the arrest and/or charges being filed against a responsible party, the Fish and Wildlife Service said. It asks anyone with information to contact its office in Madison.