I wrote my senior thesis on lynching spectacles.

Were lynchings simply not prosecuted?

No, generally they were not prosecuted. Lynchings were seen as necessary measures taken by white men to protect white women and white communities from black men who they perceived to be sexual predators.

For example, if you watch the film "Birth of A Nation", the Klu Klux Klan avenge the suicide of a white woman who died protecting her honor from a roving black man and the white men are portrayed as heroes for doing so. Protecting white women from rapes (rapes that statistically almost never happened) was the biggest reason for the lynchings, and racial anxieties over the new relationship between white southerners and freed Blacks also played into it.

For the first time, many black men were traveling around to urban centers looking for work that was often seasonal. Lynchings happened in areas that were only 25% black compared to places where the Black population was large. This anxiety over black men and the new racial hierarchy and 'unprotected' white women created the perfect excuse for killing black people using mob violence.

How were people able to participate in a hanging without fear of incarceration?

In many cases, the local law enforcement took part in it, or at least gave up Black suspects to lynching mobs. They either believed in the justification of lynching or didn't want to get involved. Sometimes mobs would turn on law enforcement that tried to stop them.

I know that there was tremendous racism at the time but a crime was still committed so did these lynchings go to trial and then get acquitted or was no one arrested at all?

In the early part of the 20th century, no attempts at arrest were made at all. Lynchings were not investigated. Then later lynchings were seen as a blight on the South, a sign of backwardness in white Southerners but still, investigating lynchings was unpopular and government officials who tried to get justice for victims would often get voted out. There was one case I found where a sheriff who was removed for taking part in a lynching got his job back only a year later.

Where was the state in all of this and how were mass gatherings able to go on without law enforcement stopping it?

Again, law enforcement was in on it. Lynchings were highly attended spectacles that could attract thousands of people from the surrounding area. It was like the circus arriving in town. You have to remember, the US had a culture of non-judicial killings for centuries before lynchings became popular, so watching a hanging was something people liked to do while having a picnic. Going to a lynching was considered much the same by the people who came... and some large lynchings were watched by Black people as well as white.

Now, I know the simple answer is racism but I’d like to know more about how this happened for so long and if there has been a recent effort to go back and prosecute those who were part of those lynchings even though they are elderly now.

Racism is the answer. Racism, gender dynamics, patriarchal views on sex, anxiety over a post-slavery society, and urbanization. You can't ever under estimate the power of hate and distrust white Southerners had against Black people after they couldn't physically control them anymore.

Yes, there were lynchings in the North but the South was way more prevalent.

Public lynchings lost popularity by the beginning of WWII. By the time the Civil Rights Era had ended and racial violence was beginning to be taken seriously, most of the participants had either died or disappeared. Also, lynchings aren't considered federal crimes so you can hardly expect racist communities to go after their own people for crimes they don't want to know about (who wants to send their granddad to jail? no one).

Books for your own research:

The Spectacle of Lynching: Rituals of White Supremacy in the Jim Crow South

Southern Horrors: Women and the Politics of Rape and Lynching

Lynching and Spectacle: Witnessing Racial Violence in America, 1890-1940

Lynching to Belong: Claiming Whiteness Through Racial Violence

The majority of my research came from examining old lynching reports from main stream news paper articles. If you are interested, I can send you the paper so you can read my examination in detail.