"someone" as the antecedent of "they"

“They [The Police] think they know who did the leaking,” the paper quoted an unnamed government source as saying. “It’s now a case of building a case that will stand up in court. It was someone with access to historical files. They went in and grabbed a range of material. It was quite crude.”

(The Guardian.)

I read "They" in They went in and grabbed a range of material as a singular pronoun meaning "he or she" in the paragraph above. Am I correct?