Once, I could agree with it being luck...maybe hit the right code, cut/ splice the right wires etc, but I doubt it.
All wiring carries anti-tamper circuits, any decent alarm engineer will rotate wiring colours throughout the installation, so it's pretty unlikely that the same wiring colours were used twice in a row.
If this is a monitored system, I would want to see a copy of the alarm centre logs for the evening. I would also be calling in a local alarm engineer to rewire and thoroughly test the entire system, and not ADT.
Incidentally, the Alarm centre will have flagged a telephone line being cut, although they will not know the reason for it.
It has been suggested already that an insider with intimate knowledge may be responsible. I doubt that is the case. Much more likely the cause lies with bad site planning and installation or poor or faulty equipment. ADT on the third occurence would be paying for re-stocking my shop or my business would be going to another company.
In any case, you would be advised to put in place additional measures to contain any break-in to one area if possible. By this I mean physical security. Make it very difficult to move around, and impossible to go from one area to another without passing at least two methods of tripping the alarm.
rgds