C I A is the general consensus of opinion

LBJ/MOB/CIA

Oswald was probably the right call. A communist who was emotionally unstable and maybe/probably mentally ill who was sneaking around in a high floor of the building alone without any reason? In the exact same place where they found bullet shells?

That said, there are good reasons to think he wasn't alone. Oswald had many connections into the communist community. And there rumors say the bullet shells where moved by the police from multiple windows in the huge room towards one window. Also many bystanders say they heard shots from multiple directions. And the destructions on the car would be easier explained my multiple shots from multiple directions rather than one bullet that penetrated everything and bounced off multiple times.

CIA Reading room: https://www.cia.gov/readingroom/search/site/jfk

FBI Vault: https://vault.fbi.gov/John%20F.%20Kennedy%20Jr.

and Wikileaks: https://search.wikileaks.org/?query=&exact_phrase=&any_of=jfk%2C+%27john+f+kennedy%27%2C+%27john+f.+kennedy%27%2C+%27john+fitzgerald+kennedy%27&exclude_words=&document_date_start=&document_date_end=&released_date_start=&released_date_end=&include_external_sources=True&new_search=True&order_by=most_relevant#results