The surviving suspect in the Boston bombings, Dzhokhar Tsarnaev, quit talking to investigators right after he was read his Miranda rights, four authorities briefed on the investigation said.

The Associated Press said the four hailed from both political parties, but requested anonymity because they weren’t cleared to talk on the case.

It’s not clear whether any statements Tsarnaev made to the FBI about his role in the attack came before or after the reading of his rights, AP reported. Specifically, he told investigators that his brother, Tamerlan Tsarnaev, was the brains behind the terror plot and only recently recruited him to participate, AP reported.

It’s not clear, either, whether investigators really need those statements to win a case against the terror suspect. AP reported that police have plenty of physical evidence that ties Tsarnaev to the attack, include a handgun and a remote-control device ostensibly used to detonate the bombs.