Does anyone know of any good true crime agents/publishers

Visit a book store. Look in the aisle that features other books similar to what you've written. Write down the publisher of the book. Write those publishers and ask the names of the agents who sold those books to them. If no agent was necessary, then follow their guidelines and submit directly.

Barring that, look in the dedication pages. See if anyone there is also listed as a literary agent in a literary guide. If so, find the agent's guidelines and follow those carefully.

This is what's known as research. Only the writer of a manuscript can do it properly because only that writer knows intimately the contents of that writer's manuscript and can therefore decide which agents handle similar material.

A search on Agentquery.com for true crime pulls up 7 pages of agents, including Stephen Barbara who was hanging out in the 'Ask the Agent' thread on this site recently.

Also take a look at QueryTracker.net, it has a database of agents similar to agentquery, but the search engine is more precise. And, after you find some agents, QueryTracker continues to be useful with other tools.