A lawyer would recommend the deserter to do this anyhow, regardless of being or not being under arrest. The events happened long ago, and at this point JAG has only limited evidence. Any lies would be contradicting that evidence. A lawyer would tell his client to be silent. In case of specific accusations the lawyer will learn the evidence and work out a response (such as "I was hit over the head with a brick on that day, and came to my senses only on airplane home," or "I was given opium in my food and became hypnotized.")
or would it automatically get a lawyer on general principal?