I have actually yet to take that course, but I worked in that field last summer so I know enough of it. Basically, because of the fear of the coercive powers of authorities and their ability to take advantage of individuals and cause them to incriminate themselves and basically to undermine the justice process, at a certain point authorities are required to read you your 5th Amendment rights and 6th amendment rights (called Miranda rights based on Miranda being the landmark case).
So if an individual is in custody and you question them and you do not read them their Miranda rights and they do not agree to waive those rights and testify, then you cannot use that information against them in a proceeding. However, that means nothing in a case like this where the weight of the evidence against the guy will probably be enough to prosecute him anyway. Therefore, the government is losing very little in questioning this guy without first reading him his rights because even if they can't use it in court because it falls out of the public safety exception, they've got enough to find him guilty regardless. They have nothing to lose.