Despite the sensationally deceptive headline, the above quote, deep in the article, IMO, demonstrates that Hoover believed Oswald acted alone and would have been convinced as such in a court of law. If this were not his belief he would not have warned the Dallas police department 4 times that Oswald's life was in danger. Rather, he would have been satisfied that Oswald were taken out if he wanted something covered up. Hoover seemed genuinely concerned about conspiracy theories and that the public might believe some malevolent group was at large.
One item not mentioned: Why did the Secret Service and/or FBI not track Oswald while the President was in Dallas? They knew who he was, what he was and that he had recently been spotted at the Cuban and Russian embassies in Mexico. Yet they did nothing?
Well, the thing is that this was 24 hours after the JFK assassination. There was, at that time, no investigation conducted yet. They had a gun, they had a suspect, they had other evidence but there were many, many unanswered questions. Even if you believe all of those questions were eventually answered and prove Oswald acted alone, there was no way Hoover could know that unless (a) he had knowledge of the case that predates the events of 11/23/63 or (b) there was some "smoking gun" evidence that has never come out but he knew it at the time. Otherwise, he's stating it is necessary to convince the public that his opinion is fact.
What we've learned is that the FBI never changes. If a muslim walks into a crowd, shouts "Allahu Akhbar!" and detonates himself the FBI will rush in and, to quell public fear I guess, announce it was a lone wolf and had nothing to do with Islam well before they know a damned thing about the guy other than he shouted it was for Islam.
Yep. If only they'd kept Oswald protected the whole conspiracy industry would never have started. It's all based on Ruby's killing of Oswald. Obviously Hoover knew Oswald's death would give birth to a flood of conspiracy rumors.