Agent Larry Chappel is an agent for the DEA. Unknown to the DEA, however, Chappel is an informant for Gideon Lyon and Tito Flores, both whom he's leaking inside information to and the rest of their cartel.
Larry Chappel is a straightforward agent of the DEA, who appears to take the job serious enough or even more serious than even the average agent who takes the job serious enough, for obvious reasons.
Chappel is first seen in Captain Avery's office giving him and his squad info on a ex-CIA agent who ended up working for the Tito Flores cartel.
As Riggs and Murtaugh and Palmer have gotten Maria and her son to safety picking her up from the airport, Chappel got found out and was then apprehended by Avery and taken into custody.