Does the Talmud mention that 40 years before the destruction of the Jewish Temple in 70 C.E. the Roman Empire had taken away from the Jews the right to execute the death penalty?
ב"ה Shalom The Gemara Shabbat (15 a) indeed says that 40 years prior to the destruction of the Bet Hamikdash the Sanhedrin went into exile and that no longer was capital punishment carried out. However, Tosafot to Sanhedrin 37b (ד"ה מיום) says there were special circumstances when they reconvened and did carry out capital punishment. See also Mishna on Sanhedrin 89a where it seems that capital punishment was carried out even after the destruction of the Bet Hamikdash was destroyed. All the best.