“The Torah says murderers should be executed…. “
If you want to require Torah criteria, then even the San Bernadino terrorists would not get capital punishment. I’m sure there were no kosher aidim, especially no warning and acceptance.
There are no judges with real Smicha, and there is no Sanhedrin of 71 sitting in the Lishkat Hagazit (which is required for a court of 23 to carry out capital punishment).