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A federal agent said WhatsApp's encryption is a lie. Then the investigation was shut down
(www.techspot.com)
This is a most excellent place for technology news and articles.
They own the (closed source) app, which has full access to your decrypted messages. The messages might be e2ee in transit, but they must be decrypted for you to read. This means that they also have access to them in this state, the same as you, and there is nothing preventing them from resending those decrypted messages back to their servers while you send them (before they encrypt) or after your receive them (after they decrypt).