A sign is posted on Fletcher Avenue for the missing cousins Lyric Cook-Morrissey, 10, and Elizabeth Collins, 8, Thursday, July 19, 2012, in Waterloo, Iowa. (AP Photo/Waterloo Courier, Matthew Putney)

The parents of two girls abducted from Evansdale four months ago have written an open letter to the girls’ kidnapper. The letter was posted on the The Waterloo-Cedar Falls Courier website Tuesday morning.

Authorities believe the girls were abducted from Evansdale on July 13, while they were on a bike ride. Hundreds of volunteers searched for the girls, and authorities also drained Meyers Lake during the search.

The letter, posted online at about 9 a.m. Tuesday, is titled “To Whom It May Concern.”

It starts by saying the families have no idea who the kidnapper is, but they know something about the person.

“Because only someone who hurts inside would hurt another person and their family,” reads the letter.

The letter talks about the pain that families have experienced, and calls on the person to be “a hero, not a monster.”

The letter asks the person to let the girls come home. It is signed by Drew and Heather Collins and Dan and Misty Morrissey-Cook.

Click here to read the letter.