It seems that if he had knowledge of the safe and the gun, knew they were related to a crime, and didn't report it to LE, then this should be enough for an accessory charge? Maybe he is not being charged because they are married (well, not legally, of course)?
Selections from
Bowen v. State, 791 So. 2d 44 (Fla. 2d DCA 2001). I couldn't find the entire case anywhere on Google.
"The State must prove that Ms. Bowen provided some maintenance, assistance, or aid to Carr after he committed each crime. Although the common law recognized the crime of misprision of a felony for failing to report a felony to authorities, the substantive law of Florida does not recognize such a crime. Holland v. State, 302 So.2d 806 (Fla. 2d DCA 1974). Thus, the crime of accessory after the fact requires some overt action by the defendant. Roberts v. State, 318 So.2d 166 (Fla. 2d DCA 1975) (holding that merely living with person, knowing that there is an active outstanding warrant for person's arrest, does not constitute crime of accessory after the fact). See also State v. Brown, 197 Neb. 131, 247 N.W.2d 616 (1976); Lowe v. People, 135 Colo. 209, 309 P.2d 601 (1957)."
"The type of overt act that will make one criminally responsible for this offense, however, is subject to some debate. In some jurisdictions, merely disavowing knowledge of a crime or of the perpetrator or his whereabouts is not enough to support a conviction for accessory after the fact. See United States v. Magness, 456 F.2d 976 (9th Cir.1972); United States v. Foy, 416 F.2d 940 (7th Cir.1969); Miller v. United States, 230 F.2d 486 (5th Cir.1956). These cases are a logical extension of the principle that a person generally has no duty to report a crime or to respond to police inquiries."
"The State must prove that any aid Ms. Bowen gave to Carr was given with the specific intent to aid him in avoiding punishment. For example, aid given to a felon to protect one's personal safety or for other personal reasons, but without the intent to assist the felon, will not support a conviction for accessory after the fact. See, e.g., Helms v. State, 349 So.2d 726 (Fla. 4th DCA 1977) (holding evidence that defendant purchased marijuana that he knew was stolen, and thus helped thieves dispose of it, was not sufficient to prove accessory after the fact to theft); Whorley v. State, 45 Fla. 123, 33 So. 849 (Fla.1903) (holding defendant, who was surety on bail bond, could not be convicted as accessory after the fact when he exercised his right to refuse to allow bonded individual to leave state to assist police in catching perpetrator of crimes). See also Maddox v. Commonwealth, 349 S.W.2d 686 (Ky.1960)."
Simply knowing a crime was committed is not enough to convict of accessory after the fact. One has no duty to report a crime, so unless there is some evidence -- and I've not heard any at this point -- that he did something like hide the safe or put the gun in the car then it would probably be a difficult charge to prove.