One dead MP is moderate. Six or more is radical. He's moderate and deserves a moderate sentence.
Many “moderates” are a bit of traditionalists, as well. How about a traditional British sentence: hanged, drawn, and quartered.
Hanged, but cut down while alive, then emasculated and disemboweled, then in some way, rendered into four parts.
The Ku Klux Klan was only ever the “Invisible Empire” because ‘decent’ White people who weren’t radical enough to join still still refused to become actively involved in ending its campaign of terrorism. Regardless whether they did this because they secretly feared retaliation from the Klan if they spoke out, or if they agreed with the its agenda, the KKK’s survival was directly beholden to their silence.
And so it is with the “moderate” Muslim. “Radical” Islam only exists because the Muhammadan community at large permits it to.