You mean like they did in the preceding paragraphs?
I don't mean to offend you in any way, but here's a quote from one of the preceding paragraphs:
> Fulton T Armstrong, a research fellow at the Center for Latin American and Latino Studies at American University, told fact-checking website Politifact.
So, the preceding paragraphs are from Politifact, not from the BBC's journalists.
> Mr Trump and Mr Sessions have pointed the finger at former President Barack Obama over the spread of MS-13, alleging that his open-door immigration policies fuelled its growth. But the gang formed and flourished in the US long before Mr Obama came to power. MS-13 was identified as a significant threat in the 1990s, and a special FBI taskforce was convened against the gang in 1994.
Then strengthen that argument with a quote taken from politifacts article.
Anyway, unless you have reasons to try to distrust politifact I don't see the problem.