The problem as I see it is why CO thought it safe to continue from EWR to DEL with this guy on board...how did anyone know what his intentions were? was it as 'simple' as a murder and thats it? How in the world did anyone know that it ended there? and that his bags were well screened? that he was not now suicidal and wanted to take everyone with him or a few sitting next to him?
He had been screened by the TSA at EWR, or are you saying you don't trust that process ? He'd also flown from PHX without incident.
if you were in this position not knowing anything except what 'the authorities' knew at that time ie that this guy murdered two people,
I don't believe there was an arrest warrant at the time, so the most the 'authorities' knew was that he was a suspect; albeit pretty much a slam dunk. We haven't seen (and probably never will) exactly what the captain was told - actually,
informed about since there was no voice comm involved AIUI.