The document noted that the NSA Signals Intelligence Directorate (SID) had neither Kumarin’s phone number nor a sample of his voice when asked by the State Department to probe possible links between the target and St. Petersburg authorities.
"The identification and collection of Kumarin's phone number was made possible by the efforts of the OCN's [US Office of Crime and Narcotics] [redacted] who worked with Math Research Group analysts to produce contact chaining charts and collection managers to optimize collection," the document explained.
The document also noted that SID acquired Kumarin’s phone number and used signals intelligence to obtain more information about the Tambov gang’s organization and structure.
The document did not specify if US officials offered to assist the Russian government with its investigation into the crime group.
In 2009, a Russian court convicted Kumarin of fraud and money laundering and sentenced him to 14 years in prison.