SciFi book search, possibly baen?

Question

I'm looking for a sci fi book I read once, sometime in the last 10-12 years. Probably published around that time, too It was an ebook, possibly/probably on Baen. Although every time I've searched since, I've failed to find it.

The premise was that a section of humanity got superpowers overnight. To begin with they were welcomed as superheroes but...as might be expected, they turned criminal, robbing banks and carving out their own empires. Possibly called Ultras, they were super villians instead. Each had a single weakness, and the book was about a group of people who tried to kill as many as possible of the ultras, identifying the weaknesses one by one. One member of the group lost his father in a bank robbery orchestrated by one of the ultras at the start of the book / when they first occurred.
It was widely believed that he was the sole survivor of the event and could identify that particular villains weakness. They even tunneled into the ruins of the bank to look for clues, and a weapon that once injured the villain (a pistol) - nothing special about it. It turns out that he could only be killed or injured if the person doing so had no ill intent towards him. He got tricked into firing the gun from previously with a detonator in the barrel and blowing himself up. It also turned out that a couple of people in the group were themselves super powered. Set in the US in the near future.

Answer 1

Could it be The Reckoners

That matches all the descriptions you gave

Twelve years ago, an object dubbed Calamity appeared near Earth and burst in the sky, emitting a strange radiation which gave a small group of humans super powers and near invincibility in apparent defiance of the known laws of physics. They all have different types of powers and weaknesses, with no apparent rhyme or reason. Dubbed Epics, these super-humans took to crime. Existing government proved absolutely incapable of controlling the Epics, the most powerful of which replaced government authority and enslaved the rest of humanity.

Ten years ago, an eight-year-old Chicago native boy named David Charleston was orphaned when the High Epic Steelheart murdered his father while fighting a rival Epic, Deathpoint, in a bank. The sole survivor of the bank carnage, David has now come of age in what is known as Newcago, ruled by Steelheart. David witnessed Steelheart's one weakness as his father inflicted a minor wound at Steelheart's eye while trying to shoot the other Epic, and David has grown up devoting his life to learning all he can about the Epics to find their weaknesses, with the goal of avenging his father. He finds "the Reckoners", an elite group led by "Professor" Jonathan Phaedrus with the common goal of killing as many Epics as possible. They decide to admit him into their group when they discover he has witnessed Steelheart's weakness, and his collected research.

Steelheart has turned most all of Newcago into steel with his power and his lieutenant Nightwielder keeps it in eternal darkness by hiding the Sun. The mortal citizenry live mostly underground and work at menial factory jobs. Yet Steelheart has proved one of the more effective Epic rulers, by providing Newcago with infrastructure, food, water, and electricity, in contrast with most other cities in what are now known as the "Fractured States".