He would not have sent anything to ISIS in advance, for fear of compromise by the FBI/NSA etc.
The scene has been more tightly controlled than any I have ever seen. Not even his driver license photo has been released! He could have left Antifa/ISIS literature all over the hotel room, his houses, and on his computer, and we may never know it.
Not unless he mailed out information packets to multiple media outlets. In that case, we might learn the truth. Otherwise, it will always be a mystery.
Travis, as I have posted before, this horrible crime and this guy's involvement with Isis or whatever will probably remain a secret like who really had JFK killed.
So, he will become another monitored/surveilled lone wolf killer.
I started to post "Hopefully, some Brit newspaper will let us know what happened. Unfortunately the Brit Newspapers are in bed with the "Don't let the civilians know what really happened!".