I would say that once the purge ends you cannot be legally married to multiple people. Meanwhile if you murder someone they're just dead. If you kidnap someone you'd have to let them go when it ends.
Stealing is an interesting gray area. Is possessing a stolen object the crime, or is the stealing the crime? Or possibly both? If possessing a stolen object is illegal then you'd have to return them when it ends.
What if you shot someone during the purge, but they did not actually die until the next day.
I'm thinking this whole "no laws" concept would actually need hundreds of thousands of laws. Courts would be tied up for years after each purge just trying to answer the legal questions regarding having no law.
Within 4 hours of announcing that a "purge night" was a thing, they would have to revise it to just call it "murder night" and even then, it will get further modified to "Murder of sanctioned people and groups night" and even THEN they will have to further amend it until it finally says "The police get to murder you night" and then they will want to remove the nightly restriction and then BAM you have what we have now.