French to English Law/Patents Idioms / Maxims / Sayings

This is one expert witness making a formal response to another. He has just said that his company had raised no objects to the experiment conducted by the other expert witness on the causes of the defects that are at issue in the lawsuit, but that they did not realize that that would be the sole basis of his opinion, when he had, in fact, been alluding to other ongoing research.

He then says:

Mais, à ce sujet, où sont les résultats de ces analyses sur les prélèvements réalisés lors de la seconde campagne, *alors que vous y étiez seul*, et sans avoir répondu à ma demande circonstanciée, par courrier électronique du XX Juin 20XX dans lequel, en réponse à votre message du XX Mai 20XX, j’écrivais ( avec copie à mes confrères) :

And this is followed by a copy of his June email.

I am not sure how to unpack this sentence, especially "alors que vous y étiez seul". I showed it to a native-speaking colleague and she said that it seemed poorly and confusingly written, and could not see who "alors que vous y étiez seul" and "et sans avoir répondu à ma demande circonstanciée" related to each other and the rest of the sentence. I am hoping someone can help me make sense of this.

Thanks in advance.