Agent Tim Donovan was an agent of the Drug Enforcement Administration.
In 2003, he and his unit were in the middle of a long-term operation against Colombian drug lord Cesar Velez, during which one of his colleagues, Agent Livia Sandoval went undercover as Livia Tellez, in which guise she became a kept woman for Rafael Zapata, the head of the New York City of Velez's cartel. When Sandoval was murdered by Zapata, then-ADA Alexandra Cabot sought Donovan for information that would allow the Special Victims Unit to get a warrant to search Zapata's yacht for evidence.
When Zapata's attorney Lionel Granger demanded that Cabot produce the source, Donovan initially refused to appear, but eventually agreed to when he learned that his refusal to show his face was causing the Velez cartel to focus its considerable wrath on Cabot instead. Sadly, Agent Donovan's identity was discovered by the cartel. The night before he was supposed to testify, a bomb is planted in Donovan's car. It exploded the second he turned the ignition, killing him instantly. (SVU: "Loss")