James Oliphant and David Savage cover the Shahzad/Miranda controversy for the LAT:
A senior FBI official said Wednesday that the agents talked to Shahzad for about three or four hours under the [public safety] exception beginning late Monday night and into the early hours of Tuesday. They then decided to read him his Miranda rights. At that point, the officials said, Shahzad continued to talk despite the warning.
The source, who asked not to be identified because the case is still active, added, "You have to make a decision on a case-by-case basis. Have you accomplished the public safety component? And you also have to make determinations on whether he's talking or not talking. So there is no hard-and-fast rule. But it has to be reasonable. You can't utilize it indefinitely.''
Still, investigators were not compelled to read Shahzad his rights.
"Miranda is not a constitutional requirement, like giving someone a lawyer," said Paul Cassell, a University of Utah law professor and former federal judge. "People who grew up watching cop shows on TV think it is more than that, but it's not."
The Supreme Court held in 2004 that law enforcement officers are not constitutionally required to issue Miranda warnings. The risk, however, is that incriminating statements, such as a confession, are not later admissible, potentially weakening the government's case.