Alan Messinger is a friend of Alexandra Cabot from her times of studying and practicing law, rising to the rank, of New Jersey ADA. Cabot asked for his favor of speaking to Matthew Linwood Brodus to get his confession for the torture-murder of Debbie Cooper. Messinger refused, as Brodus' execution was days away.
When Cabot took it to the courts, with Messinger defensing the New Jersey offices, Cabot won the case. Messinger accompanied her, Stabler, and Huang to interrogate Brodus hours before his confession. Cabot and Messinger had to be sequestered to the audience room for the execution chamber when Brodus nearly killed Huang and Stabler, only to be beaten into a coma by guards. Messinger was let down Brodus wouldn't be executed, as sick and injured prisoners are legally protected under ethics clauses, and blamed the New York district. (SVU: "Execution")