Robert O'Ryan was arrested last March (09) after he attempted to break onto the Los Angeles set of Dancing With The Stars, where Johnson was a competitor.
Authorities later found duct tape, a shotgun, a handgun, a knife and a bulletproof vest in his car, and he was charged with felony stalking, felony commercial burglary and two misdemeanour counts of carrying a loaded firearm in his car.
An attorney for O'Ryan argued her client was not a stalker but merely had a "crush" on Johnson, telling the court during a previous hearing, "He was a fan inspired to come to Los Angeles with all of his possessions."
The suspect, 36, was due to stand trial for the two felony charges on Tuesday (08Jun10) but pleaded insanity on Monday (07Jun10), leaving his fate in the hands of Los Angeles Superior Court Judge Michael Pastor, who will determine whether or not he is sane and guilty.
If convicted, O'Ryan faces up to six years behind bars. However, Pastor warned he could be held by medical authorities for a much longer period if he was convicted and proved to be insane.
Johnson, 18, was expected to testify in the trial.