BERLIN (AP) — Hundreds of police officers are searching for a girl who went missing in Berlin last month, in a case that has distressed the country.

German news agency dpa reported that 100 officers were sifting through a forest 30 kilometers (18 miles) southeast of the capital on Friday.

The search comes after investigators said earlier this week that the 15-year-old, only identified as Rebecca, was probably no longer alive and that her 27-year-old brother-in-law was a suspect in her disappearance.

The brother-in-law has been detained but is refusing to cooperate with investigators. Rebecca's family says he's innocent.

Police received more than 700 responses from the public after asking for help. In particular, they're trying to find out why the brother-in-law drove to eastern Germany on the day Rebecca disappeared.