During the 1948 war, Zettler commanded Lehi forces in Jerusalem. He took part in the April 1948 attack on Deir Yassin, a hilltop village overlooking western areas of Jerusalem and the Tel Aviv-Jerusalem road. The attack by Irgun and Lehi forces resulted in a battle that ended in the deaths of about 100 villagers and 5 Jewish fighters, and spread a wave of fear through other Arab communities in Palestine. This is considered a major turning point in the 1948 war.