EVANSDALE (AP) — Authorities searching for two young cousins drained an Iowa lake Tuesday after FBI dogs detected the girls’ scents near where their bicycles were found four days earlier, heightening suspicion from family members that they might have been abducted.

FBI spokeswoman Sandy Breault said the reaction from the dogs Monday night indicated a “strong possibility” the girls had been at the lake, less than a mile from their grandmother’s house where they were last reported seen Friday. However, Breault said because there were no confirmed sightings at the lake, authorities couldn’t be certain.

Chief Deputy Rick Abben of the Black Hawk County Sheriff’s Office said the case was still considered a missing persons investigation. The decision to drain the lake was made to rule out the possibility the girls were in the water, he said.