I believe you can sue separate "agents" when they are working outside the scope of their employment under a theory titled: "BIVENS". However, not many cases have won, and those particular agents had to do harm to you directly. In that instance the COMPLAINT would have to be amended and you would have to add each one that did you harm in ONLY Their "INDIVIDUAL CAPACITIES", in the "color of authority". (don't ask me what that means, because I barely know, but you can look it up and get familiar with the term)

Not many Bivens claims have won, or they were settled, because I cannot find them. It is based upon a case Bivens v. Six Unknown Named Agents, 403 U.S. 388 (1971) This link will explain what the case was about:http://en.wikipedia.org/wiki/Bivens_v._Six_Unknown_Named_Agents

This is the link which is the "actual" Supreme Court Case:
http://supreme.justia.com/us/403/388/

I believe the "TORT EXEMPTION" you are speaking about comes under 28 USC 2680(h) which states:

(h) Any claim arising out of assault, battery, false imprisonment, false arrest, malicious prosecution, abuse of process, libel, slander, misrepresentation, deceit, or interference with contract rights: Provided, That, with regard to acts or omissions of investigative or law enforcement officers of the United States Government, the provisions of this chapter and section 1346 (b) of this title shall apply to any claim arising, on or after the date of the enactment of this proviso, out of assault, battery, false imprisonment, false arrest, abuse of process, or malicious prosecution. For the purpose of this subsection, “investigative or law enforcement officer” means any officer of the United States who is empowered by law to execute searches, to seize evidence, or to make arrests for violations of Federal law.

The Bivens Claim does goes outside the parameter of the "Tort Claim", and is the only Alternative to it, but it only applies to "Individual Government Employees" working in the color of authority, and you better be able to prove that that particular person harmed you directly, or don't bring the claim.

If a State employee harmed you in their individual capacity, it would fall under 42 USC 1983, which is the State version of the Bivens claim(s). That Statute states this:

 
                 TITLE 42--THE PUBLIC HEALTH AND WELFARE
 
                        CHAPTER 21--CIVIL RIGHTS
 
                         SUBCHAPTER I--GENERALLY
 
Sec. 1983. Civil action for deprivation of rights

    Every person who, under color of any statute, ordinance, regulation,
custom, or usage, of any State or Territory or the District of Columbia,
subjects, or causes to be subjected, any citizen of the United States or
other person within the jurisdiction thereof to the deprivation of any
rights, privileges, or immunities secured by the Constitution and laws,
shall be liable to the party injured in an action at law, suit in
equity, or other proper proceeding for redress, except that in any
action brought against a judicial officer for an act or omission taken
in such officer's judicial capacity, injunctive relief shall not be
granted unless a declaratory decree was violated or declaratory relief
was unavailable. For the purposes of this section, any Act of Congress
applicable exclusively to the District of Columbia shall be considered
to be a statute of the District of Columbia.

If you want to pursue this, you will need to read, read and read some more of cases, statutes, etc. You can do it, but remember, there is always a price to pay for what you believe.

I hope the aforementioned information helps you.