Remember that plagiarism is the practice of taking someone else's work or ideas and passing them off as one's own. Quoting, even quoting without giving the author, isn't plagiarism. Claiming someone else's thoughts, words and ideas, as your own, that's plagiarism.
I do wish that plagiarism was easier to spell. At school, my English teacher would underline my misspelling of the word, often with the expression, written in red ink for emphasis, "See me!" Oh sh*t!"
		
		
	 
I shouldn't have used the word "plagiarism" in the thread title as I've since tried to acknowledge, but couldn't think of a better word to explain someone drafting two statements and getting someone else to sign one of them as though they were their own thoughts, (what would you call that, a "cock and bull story" if both were equally inaccurate I suppose, or "speaking for someone else" albeit non-verbally?).
Moving on I've spent more time examining the statements I've quoted from above, (in fact there are three statements signed by these two people each).
I've tried to look at whether they introduce issues in their statements in the same order, and whether they are saying the same things, even before similar or the same grammatical errors and phraseology is considered. 
They are saying the same things, very much so, signed at the same time in two of the three statements, and the third ones two months apart. Now I know if two people witness the same event then you would expect or desire to see consistency wouldn't you, but if some of the events being described were not witnessed by either, (hence both relying on hearsay), or one of the two didn't witness the event being described, then this is a different matter.
I do think a bit of assistance, probably from a professional of some kind, (maybe a police officer, as they have to assess statements all the time dont they, ...., I do know a few retired officers who might be willing to give me a few pointers).