So why did they start with the “knife” lie?
I think you have to allow for the possibility of confusion before going straight for conspiracy.
I tend to think their approach -two Boston cops and one FBI agent, meeting by themselves with this guy in his apartment at night, supposedly - was risky and they probably got taken off guard by his attack because things seemed to be going ok.
I think the Boston police have actually been pursuing the murder case and possibly they had an FBI agent with them to see if the guy had also participated in the bombing. The FBI is famous for doing investigations in a different jurisdiction without informing the locals, so I wouldn’t read too much into that. And if they wanted to cover up his participation in the bombing, they wouldn’t have shot him before he signed the statement.
Another possibility is that he got hold of somebody’s gun, or possibly his own, and attempted to shoot himself rather than sign the statement.
All sorts of things are possible, I guess.
Because they were too afraid to admit they got their *sses kicked by an unarmed man.