Most likely one of three possibilities. Attached to the actually key switch are two small usually light green switches, one may have gotten broken moved etc during the theft.
2: that particular relay has sticky contactors inside and needs to be replaced.
3: inside the steering colum cover at the ignition switch and gear shifter there is a stop the prevents the key from being turned to the run position if the shifter is not completely in the park position. I could have gotten bent or mis aligned during the theft.