WASCO, Ore. (AP) _ A man walked into the unlocked house of a co-worker Tuesday and fatally shot 2-year-old girl in her mother's arms, officials said.

The mother, Shelly Middleton, wasn't injured, but suffered a breakdown and was hospitalized, said Sherman County Sheriff Gerald Lohrey.

The gunman spoke to the woman before shooting Mandy Middleton, Lohrey said. But the sheriff declined to reveal what was said.

Mrs. Middleton and neighbors in the town of 445 people in northern Oregon provided a description of the gunman's pickup.

Gregg Goff, 24, of The Dalles, was arrested about two hours later in Klickitat County, Wash. Lohrey said he was booked on suspicion of aggravated murder.

Goff and the child's father, Rob Middleton, worked for Columbia Aluminum in Goldendale, Wash., and had gone hunting together in the past, Lohrey said.

The sheriff said he had no evidence of any disagreements between them. ''I don't have any motive at all,'' he said.

Middleton had gone to work and was not home at the time of the shooting, Lohrey said.