Albert Barnes on Matthew 26:5

Not on the feast day. Not during the feast. The feast lasted seven days. A vast multitude attended from all parts of Judea. Jerusalem is said to have contained at such times three millions of people. Amidst such a multitude there were frequent tumults and seditions; and the sanhedrim was justly apprehensive there would be now, if in open day, and in the temple, they took away a teacher so popular as Jesus, and put him to death. They therefore sought how they might do it secretly, and by guile.