‘And they watched him, and sent out spies (or ‘ambushers'), who put on a pretence that they themselves were righteous, in order that they might take hold of his speech, so as to deliver him up to the rule and to the authority of the governor.'
This verse beautifully sums up the true situation. These men who approached Jesus, who were sent by the Sanhedrin who waited out in the darkness, and pretended to a great deal of righteousness and godly concern, were actually tricksters whose one aim was to catch Him out and report Him to the governor for subversion. They wanted to entrap Him into saying something seditious, i.e. that ‘it was not lawful to pay tribute to Caesar'.
Mark tell us that they were an unholy alliance of Pharisees and Herodians (Galilean court officials), but Luke does not want to complicate things for his readers, who would know nothing of the Herodians (see Mark 12:13 and compare Mark 3:6).