It should be no surprise that they would attempt to seize him. A part of the people attending his judgment clearly continued to want his execution. Nephi would have gone to these to preach repentance, for there was no reason to preach to those who had already come to believe. Thus he returns to the very people who had wanted him killed, and said to them the very thing for which they wanted to kill him. No wonder they continued to desire to kill him, and therefore were ready to imprison him.