Just a guess, but I would assume that they won't be able to give you any more information than what is in the report. So if they asked for a letter of request for the report from you, then all you need to ask for is the report. But be careful about asking too many questions....they may question your motives for wanting the report in the first place. Send the letter requesting a copy of the report and then if you have further questions, then ask.
I don't know how CPS works, but DS's dad filed a complaint against me here in IA back in 1993, then took off with DS to CA without my knowledge (while I was at work). The basis of his complaint was alledged bruises, but he told the intake worker that it supposedly happened 2 weeks prior and had no physical proof........which told DHS right off that it wasn't credible. So when I contacted DHS by phone, one of the first things they told me was that if the report is unfounded, it is destroyed in one year. For them to be so adamant in telling me that immediately said to me they didn't consider it a credible case. And one year later, I received notification from DHS that the report had been destroyed.