It was announced that hundreds of border agents have been arrested over the years. For what?

As a border patrol agent, I was offered sex or money as a bribe to let someone go, almost every day. Often an alien is carrying drugs or valuables, which would be easy to pocket if you were so inclined.

There have been hundreds of thousands of agents over the years, and a small percentage have taken bribes and been charged with it.

More than 500 employees of the United States’ primary border security agency were charged with drug trafficking, accepting bribes and a range of other crimes over a two-year period.

Probably helping to smuggle.

Making the Demon-rats and the 9th Circus Court unhappy.
But there may be other rare reasons that have occurred.
Then there are the corrupt.

Evidence please. I think you are lying.

Corruption possibly, or framed for not going on the take like the rest.

Who announced it and where was it announced? That would be helpful in making an informed speculation.

Rape and murder