Anthony O'Neill

Detective Anthony O'Neill testified for the prosecution at Brendan Dassey's 2007 trial about interviewing Dassey in his police car on November 6, 2005. On Day 4, he described how he recorded the conversation, noted that some nonverbal responses could not be heard on the audio, and discussed his limited knowledge of the investigation at the time. The interview recording was played and admitted as Exhibit 201. When the defense objected to yellow highlighting in the displayed captions, the judge allowed it but instructed jurors to rely on the audio if the two differed.

On cross-examination, defense counsel used O'Neill's report and the interview transcript to test his recollection and questioning. O'Neill said he had not known Dassey's abilities or usual demeanor before the interview, but denied finding that Dassey had trouble understanding questions. He distinguished his report's description of confronting Dassey over an answer from being confrontational. He acknowledged that investigators had no basis for saying Halbach needed daily medicine and that he told Dassey going to jail was not going to happen; he characterized the first statement as investigative deception and did not consider the second a promise. He also agreed that an officer first raised the possibility of Halbach entering Steven Avery's trailer and that one trailer question was leading, while disputing counsel's suggestion that this was a theme throughout the interview.

On redirect, O'Neill said the medical-need suggestion was intended to elicit information about whether Halbach was alive or injured, and he said Dassey resisted the trailer suggestion. On recross, he addressed limits on his knowledge of and contact with Dassey. His testimony placed the recording and the methods used to obtain Dassey's answers before the jury without resolving the defense's challenge to their reliability.