"lawless men" were the Romans. But Pilate is not mentioned. And the author of the Peter's speech in Acts knew probably the Gospel of Marcion, since Acts is a reaction against Marcion.
It is therefore unlikely that Tertullian had the original version of Marcion's Luke, or at least he didn't know what Marcion believed about the identity of who killed Jesus on earth.
Hence the original evolution of the stories was the following:
- Before: a positive portrayal of Gamaliel the Pharisee: he calmed the Jewish opposition.
- Implications: the death of Jesus was not connected with Jerusalem. This fits Paul's ignorance about a crucifixion of Jesus happened in Jerusalem. Gamaliel's support is fabricated evidence that the early Christians were not heretical Jews (hence, by inference, in the real past what had taken place was that the mainstream Jews were accusing/cursing the Christians of heresy).
- After: a negative portrayal of the sinedrites, who accused Jesus before Pilate.
- Implications: the death of Jesus was now connected with Jerusalem. Gamaliel is never mentioned. No compromise with mainstream Jews. Pilate is mentioned.
The evolution described above explains the curious anomaly of sinedrites killing Jesus and not killing Peter, too.