If you're suggesting that more thorough vetting of Muslim immigrants could have prevented this incident, you might not be aware that the suspected bomber was born in the UK.

I was aware, but the question remains, were Abedi or one of his cousins from Syria to decide to immigrate to the US, would it be racist to thoroughly vet them before letting him in? Possibly even checking with British law enforcement. Abedi was reportedly on their radar.

Abedi's parents were from Libya, so it's unclear whether he had any "cousins from Syria." In any event, the scope of your question isn't clear. Is it racist to "thoroughly vet" any immigrants from Great Britain? No, I suppose not, but it would probably be bad policy. I'm certain that US immigration checks with British law enforcement already concerning any immigrants from that country, so again, it's not clear what you're advocating. As you must be aware, all immigrants from Syria - which you mentioned but doesn't have any specific connection to this case - are already thoroughly vetted.

No, Syrians coming into the US are not thoroughly vetted. While our vetting process has improved somewhat over the last few months, the US is not nearly as efficient as Israel in evaluating immigrants who fit the profile of terrorists. Europe has been setting the example of what not to do for two decades. The fact that Abedi was a British citizen should not mean that he should be able to waltz through US customs. Where his cousins come from, if he has any, makes zero difference. I was making a point which you apparently don't get. It was bad policy for British leaders to allow one of their own citizens, who they were apparently watching, plan and carry out this bombing right under their noses. We need to flush political correctness here and increase the scrutiny which which we evaluate middle eastern immigrants and citizens from western countries and those already here who fit the profile. This will not eliminate the threat, but it will reduce it.

"Every refugee goes through an intensive vetting process, but the precautions are increased for Syrians. Multiple law enforcement, intelligence and security agencies perform "the most rigorous screening of any traveler to the U.S.," says a senior administration official."

http://time.com/4116619/syrian-refugees-screening-process/

Sounds thorough to me.

I have no idea if he could have "waltzed through US customs" and neither do you. If you're suggesting that all Muslims should get the kind of vetting described in the linked article before entering the US, that's obviously not going to happen, and for good reason.

When you say it was "bad policy" for Britain to "allow" the bombing, that suggests that you believe British authorities could have stopped it and chose not to. If that is indeed what you're implying, that is a truly repugnant suggestion.

What extra scrutiny beyond that described in the article linked above do you recommend?

Study Israel's visitor security system for guidance on adequate scrutiny. If you fail to see galactic room for improvement on how the British and Europe generally have been handling identified terrorist threats, then get used to these annoying incidents in a city near you. I doubt that you know how much attention is paid by immigration authorities to a male 22-year-old Muslim with a British passport. Do you want to bet the life of your daughter that it is adequate? I don't. And it is repugnant that there are people defending obviously failed security when the consequences are bloody massacres.