This 'report' just doesn't sit right with me.
How was it determined that a ball-pein hammer had been used?
How was the window accessed?
Cockpit window - which one?
"Smashed out" or smashed in?
Mower-caused damage is most unlikely.
Windscreen glass (laminated) can crack overnight due to significant temperature variations after a previously undetected impact.
Toughened glass windows (unlikely to be used on aircraft cockpits) will shatter if impacted in the right place.
There are much easier and quieter ways to sabotage an aircraft.
I'm afraid, lilflyboy, that this 'report', on the basis of the information you've provided, doesn't have much credibility.