פירוש על עבודה זרה 30:14

Dimi b. Abba extends the prohibition of selling weapons to Jewish robbers. The Talmud explains that this refers even to a robber not known to murder. The robber referred to here is even one who is sneaky, more of a thief than a robber. The thief may not intend to murder, but if he gets caught, he might commit murder in order to save himself. Therefore, one should not sell weapons to them.