Day 15 in the Delphi murders trial Monday was the fourth featuring defense witnesses in the case against Richard Allen, 52, of Delphi, accused of the 2017 murders of eighth-graders Abby Williams and Libby German.

Attorneys for Delphi murder suspect Richard Allen continued presenting to jurors Monday in Carroll County as the trial began its third full week.

The defense team's expert called into question the investigation by an Indiana State Police expert. Jordan Smith, Alex Martin and Jenny Porter Tilley

Attorneys call three witnesses in defense of Richard Allen. He is accused of killing Libby German and Abby Williams in February 2017 near the Monon High Bridge in Delphi.

The defense again focused on Richard Allen’s mental health while in custody and attempted to cast doubt the state’s key evidence involving the “unspent bullet” found at the crime scene on Day 16 of testimony in the Delphi murders trial.

Dr. Polly Westcott testified for the defense that prolonged isolation and lack of meaningful contact with his wife aggravated Allen's mental illness

For the first time in the Delphi murders trial, family members of Richard Allen were called to the witness stand. Allen is charged with multiple counts of murder after teenage girls Abby Williams and Libby German vanished on Feb.

The mental health of the suspect accused of killing two teenage girls in Delphi, Indiana, was the focus of the trial as it went into a third week.