We can't prove that he was put there by anybody. That's the problem. However the convenience of his being employed there, so close to the assassination, sounds the warning bells, in my mind. Just because we can't prove who and why he was put there, doesn't mean there wasn't a conspiracy.
Ray, he may not even have been put there on purpose.
Who said that a conspiracy already had a solid and completely worked out plan in mind, months, or even weeks, prior to the assassination? Yet, that's what LNs seem to imply. If there was a conspiracy, there may well have been some sort of master plan in place, known to only a few people and able to be put into action at short notice based upon the actual circumstances at the time.
There are those who believe there had already been two previous attempts to execute the plan, in Miami and Chicago, which both failed. Perhaps it was just a case of third time lucky with all the variables falling into place in Dallas.