Who were Enrico Mantoli's friends and associates?

In the story, Enrico Mantoli is an orchestral conductor. He is murdered early in the story. Below is a list of Enrico Mantoli's friends and associates.
The Endicotts: The Endicotts are friends of Enrico Mantoli. In the story, Enrico's daughter, Duena, is their house guest. The Endicotts hear about Enrico's death after Sam Wood (a Wells police officer) visits them. In the story, Mr. George Endicott is a member of the the Wells city council. He is also the one who identifies Enrico Mantoli's body at the morgue.
Eric Kaufmann: Eric is Enrico Mantoli's associate and manager. After Enrico's death, Eric is chosen to be the administrator of the festival activities. Before long, he leaves for Atlanta to locate a new conductor for the Wells music festival. Later, Eric applies for a gun permit, citing his fears about being the next target.
At the end of the story, Mr. Endicott announces that Eric has been picked to conduct the music festival at Wells.
Frank Schubert: Frank is the mayor of Wells and the chairman of a committee that runs the city's affairs. He also owns two gas stations and runs a hardware store. Since he is the mayor, Frank would have been acquainted with Enrico Mantoli before the latter's death.
In the story, Frank advises Chief Gillespie to let Virgil Tibbs investigate Mantoli's death. According to Frank, Chief Gillespie will benefit either way. If Tibbs fails, Chief Gillespie is off the hook. Meanwhile, if Tibbs succeeds in finding Enrico's murderer, Chief Gillespie will get the credit for it.
Mr. Dennis, Mr. Shubie, and Mr. Watkins: All three are councilmen of Wells and would have been acquainted with Enrico Mantoli before the latter's death. Enrico was in charge of planning the music festival. At some point, he would have had interactions with the three councilmen.