Translation:They have executed the spy.
Unfortunately, that is not a possible interpretation of this sentence. The lu- prefix is only used when the subject is plural ("they") and the object is singular ("him/her/it"). So there can only be one spy executed if using the lu- prefix. To say, "They have executed spies," you would use the null prefix (the absence of a prefix): ghoqwI' muHta'. Note that this sentence could be interpreted as, "They have executed spies," "he/she/it has executed spies," "he/she/it has executed a spy." But, the variation it can't mean is, "they have executed a spy," which must use the lu- prefix.