Alex Radziwill is a Diplomatic immunity and State Department official who has collaborated with the team on various cases.
Due to his role in the State Department, he is often required to thwart Booth and Brennan by telling them how international law and foreign policy obstruct what they want to do; but the character is sympathetic, and it is made clear that he is not merely an officious bureaucrat, but a good-hearted person who is sympathetic to the FBI team in wishing justice to be done.
In "The Girl in Suite 2103", he becomes involved when a case leads the team to investigate a bombing in a room next door to diplomatic visitors from Columbia. When the team discover that Columbian judge Dolores Ramos murdered Lisa Winokur after Lisa slept with Ramos' son, they turn over the evidence to the state department so that Radziwill can give Dolores the option of waiving diplomatic immunity and being charged in the U.S. or handing the information on to the Columbian Attorney General so that she would be charged in her native country and sent to prison among the various drug cartels she had put away.
In "The Survivor in the Soap", Radziwill consulted with the team on the murder of a former child soldier from Sierra Leone who had received asylum in the U.S. After they found a group of other Sierra Leone immigrants attempting to escape the war, Booth ensured the cooperation of the immigrants by telling them that Radziwill would help them receive official asylum while they dealt with the murder.
In "The Lost Love in the Foreign Land", Radziwill helped the team investigate the murder of an undocumented immigrant, subsequently helping the team by arranging for other victims of the exposed human trafficking ring find asylum in America after their presence was made official. After Sun Dae Park confesses to murdering the victim's father in his home country, Radziwill informs Booth and Aubrey that he will have to deport the man to face the murder charges in his home country despite the fact that he was protecting his fiancé. The two remind Radziwill to at least ensure Sun is treated fairly and he tells them to find the true killer or Sun will end up convicted and executed for the murder of his fiancé. After Tammy Hyun confesses to killing the victim to protect her daughter, Radziwill is shown to be just as emotionally effected as Booth, Brennan and Aubrey.
- Radziwill's status as a little person is a plot point in his first episode- such as Bones commenting that Booth is being less confrontational to avoid hurting Razdiwill's 'tiny feelings', clarifying that she was referring to his feelings about being tiny rather than meaning that his feelings were tiny- but afterwards is not important to the role.
- In The Lost Love in the Foreign Land, when his role in the State Department is commented upon by a suspect due to his size, Radziwill tells her that "they need someone low to the ground to deal with the bottom feeders."