AMSTETTEN, Austria, May 16 (UPI) -- Austrian police say the man charged with fathering seven children with his daughter waited until his wife was away to get medical attention for a child.

Investigators found a postcard sent from Italy by Josef Fritzl's wife and dated April 21, The Telegraph reports. Two days earlier, Fritzl took his daughter, Kerstin, 19, to a hospital.

The delay may have cost Kerstin her life. She remains in an artificial coma suffering from multiple organ failure, officials said.

Fritzl allegedly kept his daughter, Elisabeth, 42, in cellar, allegedly sing her as a sex slave. Three of their seven children remained with their mother, three were brought up by Fritzl and his wife and one died soon after birth.

Rosemarie Fritzl apparently believed her husband's story that Elisabeth had run away from home and that she had left three children on their doorstep.

Her postcard from Maggiore was upbeat: "Dear family, my holiday has been lovely. Although I'm really busy every day, I fall into bed dead tired, but I'll soon be home, Love Mama."