29 U.S. Code § 1105 - Liability for breach of co-fiduciary
(a) Circumstances giving rise to liability
In addition to any liability which he may have under any other provisions of this part, a fiduciary with respect to a plan shall be liable for a breach of fiduciary responsibility of another fiduciary with respect to the same plan in the following circumstances:
(1) if he participates knowingly in, or knowingly undertakes to conceal, an act or omission of such other fiduciary, knowing such act or omission is a breach;
(2) if, by his failure to comply with section 1104 (a)(1) of this title in the administration of his specific responsibilities which give rise to his status as a fiduciary, he has enabled such other fiduciary to commit a breach; or
(b) Assets held by two or more trustees
(1) Except as otherwise provided in subsection (d) of this section and in section 1103 (a)(1) and (2) of this title, if the assets of a plan are held by two or more trustees—
(B) they shall jointly manage and control the assets of the plan, except that nothing in this subparagraph (B) shall preclude any agreement, authorized by the trust instrument, allocating specific responsibilities, obligations, or duties among trustees, in which event a trustee to whom certain responsibilities, obligations, or duties have not been allocated shall not be liable by reason of this subparagraph (B) either individually or as a trustee for any loss resulting to the plan arising from the acts or omissions on the part of another trustee to whom such responsibilities, obligations, or duties have been allocated.
(2) Nothing in this subsection shall limit any liability that a fiduciary may have under subsection (a) of this section or any other provision of this part.
(A) In the case of a plan the assets of which are held in more than one trust, a trustee shall not be liable under paragraph (1) except with respect to an act or omission of a trustee of a trust of which he is a trustee.
(c) Allocation of fiduciary responsibility; designated persons to carry out fiduciary responsibilities
(1) The instrument under which a plan is maintained may expressly provide for procedures
(A) for allocating fiduciary responsibilities (other than trustee responsibilities) among named fiduciaries, and
(B) for named fiduciaries to designate persons other than named fiduciaries to carry out fiduciary responsibilities (other than trustee responsibilities) under the plan.
(2) If a plan expressly provides for a procedure described in paragraph (1), and pursuant to such procedure any fiduciary responsibility of a named fiduciary is allocated to any person, or a person is designated to carry out any such responsibility, then such named fiduciary shall not be liable for an act or omission of such person in carrying out such responsibility except to the extent that—
(A) the named fiduciary violated section 1104 (a)(1) of this title—
(3) For purposes of this subsection, the term “trustee responsibility” means any responsibility provided in the plan’s trust instrument (if any) to manage or control the assets of the plan, other than a power under the trust instrument of a named fiduciary to appoint an investment manager in accordance with section 1102 (c)(3) of this title.
(d) Investment managers
(1) If an investment manager or managers have been appointed under section 1102 (c)(3) of this title, then, notwithstanding subsections (a)(2) and (3) andsubsection (b) of this section, no trustee shall be liable for the acts or omissions of such investment manager or managers, or be under an obligation to invest or otherwise manage any asset of the plan which is subject to the management of such investment manager.