Mateen's wife knew what he planned, but didn't report it. There should be a life sentence for that.

[Mandos the Judge]

15. Possible, but...

Possible, but still a reach, since apparently he regularly visited the club in secret, which would be difficult to reconcile with the notion that he needed to do recon in the first place. From what I've read in the news, her involvement is the following:

1. Mateen expressed a general intent to commit a jihadist attack on US soil. She apparently tried to dissuade him from doing so.
2. Mateen once asked her to drive him to then Pulse ‘so he could scope it out’. Unknown if he told specifically her he wanted to scope it out for an attack or if he said something in the line of “Hey, can you drive me to the Pulse? I want to check it out.” Unknown when exactly this occurred and difficult to reconcile with several witness reports claiming Mateen was a regular visitor of the Pulse.
3. She may have accompanied Mateen when he legally purchased arms and ammo a few days for the attack. Unknown if she knew at the time he purchased these for the impending attack. Of course, even if she knew he intended to use these for an attack it’s hard to see how her mere presence during the purchase could be constructed as involvement in a conspiracy or aiding and abetting in the legal sense.
4. When Mateen left she suspected he intended to carry out an attack and tried to dissuade him. Mateen just told her he was going out with friends.

Keep in mind that knowing or having a suspicion that someone is going to commit a crime and not reporting it, isn’t a crime of itself. A conviction for misprision is unlikely, unless evidence appears that she actively concealed knowledge of the pending crime, which doesn’t seem to be the case so far. I suspect the media circus and severity of the crime may well result in charges being filed and possibly even a conviction (people will want their pound of flesh and with Mateen dead Salman is the next best thing), but from a legal point of view it’s a rickety case at best, which is probably one the reasons authorities have been slow to press charges against her so far.