The planning phase of an investigative interview is crucial, allowing interviewers to plan how to establish rapport, develop appropriate questions, and identify key information to gather. This study aimed to establish best practice for planning suspect interviews and to create gold-standard examples for two fictional scenarios. Using a Delphi method, 21 international experts on investigative interviewing participated in three rounds of data collection. Their recommendations covered structuring interview objectives, topics, and developing appropriate questions to encompass relevant hypotheses while maintaining an open-minded approach. A gold-standard template for open-minded objectives, first questions and topics to cover was achieved. These findings can assist interviewers demonstrating how to plan investigative interviews with suspects to avoid prejudicial cognitive biases, improve their interviews and achieve better outcomes. Additionally, trainers could use the gold-standard templates to teach and assess trainees, promoting high standards in investigative interviewing.