Michael Adebolajo, 29, and Michael Adebowale, 22, are accused of running over soldier Lee Rigby in a car then hacking him to death with a meat cleaver and knives.
Their trial at England's Old Bailey central criminal court in London is heading to a conclusion, with the prosecution summing up its evidence today.
Judge Nigel Sweeney told jurors that Adebolajo's evidence did not amount to a defence in law to murder.
He told the jury that the charge of conspiracy to murder a police officer, which both defendants faced, had now been dropped.
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They remain accused of murdering Rigby and the attempted murder of a police officer on May 22 this year.
The trial has heard they tried to decapitate Rigby in broad daylight outside his barracks in Woolwich, southeast London, to avenge the deaths of Muslims abroad.
In his closing speech today, prosecutor Richard Whittam said: "Islam, one of the world's great religions, is not on trial."
The jury were shown again images of bloodied knives, and a video clip showing Rigby being knocked down by a car and then dragged into the road.
"Is this a humane killing?", Whittam asked.
"Is this a killing with an attempt to decapitate and then deposit the body in the middle of the road?
"What was the purpose of what they have done, killing Lee Rigby in the way the had done, in putting the body there and staying at the scene?
He concluded: "What these two men did, crashing their car and breaking the back of Lee Rigby and then killing him is indefensible in the law of this country.
"Killing to make a political point, to frighten the public, to put pressure on the government or as an expression of anger is murder and remains murder whether the government in question is a good one, a bad one, or a dreadful one."
The defendant's lawyers were later due to sum up their case.