Air Carrier flight crew reported departure without required Hazmat documents onboard. Flight crew 'hypothesized' closeout agent accidentally removed the documents.
Synopsis
Air Carrier flight crew reported departure without required Hazmat documents onboard. Flight crew 'hypothesized' closeout agent accidentally removed the documents.
Narrative
We were waiting for three lost cans to be loaded. We had already received and signed the DG (Dangerous Goods) paperwork with W/B (Weight and Balance) number 1. W/B number 2 came across the wire and then we had a gate agent hand us another round of DG paperwork. We discarded the version 1 DG paperwork and signed the 2 DG paperwork. I signed the paperwork on top of the striped DG manifest. Then my First Officer and I started a performance data amendment due to a change in CG (Center of Gravity) for W/B number 2. I placed all of the paperwork on the center pedestal; on top of the printer. As we finished up the paperwork; we spoke with our agent about the delay and he seemed extremely concerned that he; being a close out agent; was going to be late for his ZZZ [to] ZZZ1 close out. He communicated this on his radio trying to get the ZZZ1 close out covered due to our 3 lost cans that had just been located and were beginning to be loaded. Fast forward about 40 minutes or so; we are in cruise flight on an intermediate level off around 20;000 [ft]. We received an ACARS message alerting us to the fact that our closeout or DG agent had; in their possession; our striped DG paperwork. I consulted with my First Officer to inquire if he still had his signed copy of the DG paperwork. He did. How that striped folder got off the airplane is still a mystery. I can only hypothesize that; due to the desire for our agent to make his closeout with ZZZ1; that he picked up our DG folder by accident and took it with him. That said; I can't speak with any authority on this issue as I; along with my First Officer; was surprised that it wasn't on the flight deck.I can only hypothesize that this event occurred due to the closeout agent accidentally taking the paperwork off the airplane. I sincerely don't recall. We were in a rush to leave and we somehow missed the fact that the paperwork had left the plane. We; as a crew; discussed that we are not going to allow the agent to touch the paperwork until it is handed off the plane at door closing. This would give us an additional chance to catch this error from occurring in the future.
Second reporter narrative
We were delayed from pushing due to missing ULD's (Unit Load Device) for our flight. While waiting; the gate agent brought our Dangerous Goods paperwork; including 2 DG (Dangerous Goods) manifests; and 1 'candy striped' DG envelope. The Captain and I verified the paperwork; and the Captain signed. All DG for this flight was inaccessible. The missing ULD's for our flight were finally located and loaded. This resulted in a new preliminary weight and balance; and subsequent DG paperwork. Another gate agent brought us new DG paperwork (DG manifest and 'candy striped envelope) to reflect the updated DG location. The Captain and I verified the new DG paperwork; the Captain signed the new DG manifest; using the candy striped envelope as a table top; and I put my copy of the signed DG manifest in my pocket. The gate agent was in a hurry to close our flight because he mentioned on his radio that he had to rush to close his ZZZ1 flight. At some point; one of the two gate agents removed the candy striped envelope prior to me closing the door. I don't want to speak for them; but I assume that each of the gate agents thought that they were removing the 'old' DG candy striped folder and not the new one.Moving forward; I will place the envelope on my yoke clip until the time I close the main entry door. That way I can guarantee that it doesn't leave the aircraft without my knowledge.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.