Air Carrier Ramp Lead reported a Dangerous Goods loading error of a parcel inadvertently left in the cargo compartment from a previous flight. Reporter attributed the error due to time pressure; load team communication breakdown; and failure to complete external security check.

Narrative

While working Aircraft X; I failed to see a DG (Dangerous Goods) [parcel] in A2 of Aircraft X. I put [in] front in A1 so I had a support person in the [cargo compartment] who I thought would have checked before getting out. I was on [Gate] XY with a XA:00 departure. I start at XZ:00 and have to scan my first bag by XZ:22. My support help was not at the gate at the start of my loading. I started with bags because I needed to make sure I met the 38 minute required by Local management.I was called into the office by the managers and they told me there was a DG (Dangerous Good) override [error] on my flight.The event occurred because the DG was never removed from the aircraft the night before. The support person who loaded the freight in A1 did not say anything about priority package in A2. I was focusing on my times for 1st bag scans and the support person was not part of the huddle before I started loading the flight because he wasn't at the gate.I had to go into a [meeting] and discuss what happened.[I should] not expect someone to do what I should have done. [I should] get verification. I need more time for first trips of the day because of the external security search I'm required to perform.