Jesus people. Read about what the "public safety exception" actually is before going all police-state-paranoid. If the FBI or police try to misuse or abuse the public safety exception to attempt to get Tsarnaev to incriminate himself then they are going to have some fun times in court and get their asses handed to them. I'm skeptical that that's what's happening. I'm also skeptical that he's not been read his rights…
"Dzhokhar Tsarnaev will not hear his Miranda rights before the FBI questions him Friday night" [id.] This implies he'll be going through a potentially long interrogation with the FBI that may be admittable as evidence, without having been given a Miranda warning. There is definitely something about this application of the "public safety exception", and the stare decisis discussed in the article, that gives cause for…
Public safety is involved because, lets see, millions of people were locked in their homes, a public curfew was in effect, the dead were piling up, and no one knew how many more bombs or co-conspirators were still at large.
They have a duty to learn the full extent of the terrorism, and protect the public, First. Then, worry about prosecuting this one guy's sorry ass.