The mother of missing toddler Ayla Reynolds said she is ready to reveal what she has been told by investigators, in hope of pressuring law enforcement officials to make an arrest. Trista Reynolds said descriptions of ‘‘horrific physical evidence’’ will appear in documents to be released online Sept. 24. She will describe that evidence again at a press conference the following day, when Ayla’s father is scheduled to be in court on an unrelated assault charge. Ayla was 20 months old when she was last seen at her father’s Waterville home on Dec. 11, 2011. Investigators believe she is dead. They have also said that Ayla’s father, Justin DiPietro, and other adults in the home know more than they are telling. DiPietro could not be reached Tuesday. State Police spokesman Stephen McCausland said the investigation remains active.