Legal Question in Criminal Law in California

Written Miranda waivers are not required.

You have obviously done some research. As you know, Miranda warnings are only required during custodial interrogations.

Your father was only arrested at the end of the questioning. If he was not in custody, no warning was required. The courts will look at all of the circumstances to determine whether he was confined under conditions equivalent to a formal arrest.

Cops often lie to a suspect, saying they will not arrest him, to avoid triggering an obligation to give a Miranda warning. The US Supreme Court says it's legal.

That's one of the reasons criminal defense attorneys tell people NEVER to talk to the cops.

It is already too late to tell him to exercise his 5th Amendment rights to SHUT UP and call a lawyer, as every cop show on TV correctly teaches. His attorney will now have to make any motions to dismiss or suppress evidence that may be appropriate, and defend the charges in court hearings and at trial, based upon all the arguments, documents, facts, evidence, witnesses, surveillance tapes, etc. All that will be available in discovery. If serious about getting him counsel, and if this is in SoCal courts, feel free to contact me.