Simone was introduced to the squad after Andy Sipowicz's former partner, John Kelly, was forced to leave the NYPD in the face of an IAB witch hunt.

It is also gradually revealed that Simone is a highly experienced and competent police officer, who had earned the rank of Detective Second Grade prior to his driving assignment.

An early bond and friendship between the partners was strong enough that Andy asked Simone to step in after John Kelly couldn't make it back to New York for Sipowicz's wedding to Sylvia Costas.

It is later learned that Bobby was a quiet kid whose passion for raising racing pigeons came from his friendship with a retired boxer (who later showed early signs of Alzheimer's), and that he had a flashy older friend named Ray DiSalvo whom he idolized—which came back to haunt him when Ray became a petty criminal and tried unsuccessfully to sell Bobby out to IAB for giving him an implicit warning to avoid a drug bust.

Although the transplant was successful and it initially seemed that Bobby would be discharged from hospital, he developed a Gram-positive bacterial infection which soon spread to his brain and other vital organs, causing a quick decline in his health.

Due to his being on immunosuppressants at the time to keep his body from rejecting the heart, his immune system was not strong enough to withstand the infection, and he ultimately died, devastating Diane, Andy, and the rest of the team at the 15th.