There was never any doubt that he did it, he was apprehended shortly after the crime splattered with the victims’ blood. However, Michael Spiegel’s defense at trial was that he was not sane at the time of the killings. The jury found him guilty in just a couple of hours.
Insanity is an affirmative defense, which means the burden is on the Defendant to prove that he was insane at the time. It’s difficult to do, especially when two people are brutally killed. There was evidence of a long history of mental illness, but the jury did not find it sufficient. The State argued that the steps he took demonstrated planning: which is indicative that he understood the nature and wrongness that he undertook. The finding today doesn’t mean that he wasn’t crazy, but that the jury wasn’t convinced that he was so mentally impaired that he did not appreciate what he was doing or that it was wrong.
There is a 25 year minimum mandatory sentence on the firearm charge. Due to his age, Mr. Spiegel will almost certainly die in prison, even if the judge doesn’t give him a life sentence.
You can read the standard Florida jury instruction on Insanity here.