(AP) — The attorney for an Omaha man charged with the shooting deaths of four people is strongly hinting at an insanity defense.

Douglas County Public Defender Thomas Riley interrogated police investigators Tuesday during the preliminary hearing for Nikko Jenkins, asking whether they were aware Jenkins might have mental health problems. The investigators doggedly rebuffed the questions, but a Douglas County Sheriff’s Office investigator said he had seen at least one reference to Jenkins’ claims to have heard voices.

Riley also grilled investigators about their interview of Jenkins, in which they say he confessed to the killings. In particular, Riley questioned whether investigators were aware that Jenkins had invoked his right to an attorney days before the interview and whether investigators lied to him about the evidence they had.