DALLAS , Texas ( CNN ) -- The FBI has seized a two-page , handwritten letter of condolence sent by Jacqueline Kennedy to the widow of Robert F. Kennedy shortly after he was assassinated in 1968 . The family contends the letter was stolen . Jacqueline Kennedy sent her sister-in-law a condolence letter in 1968 which is now in the hands of the FBI . `` We 're trying to determine who the legal owner is , '' said Mark White , a spokesman for the FBI . `` There 's still an ongoing investigation . '' The letter 's path from the Virginia home of Robert Kennedy 's widow , Ethel Kennedy , to a locked evidence vault in the Dallas field office of the FBI is described in a six-page affidavit filed last month in U.S. District Court in the Northern District of Texas by Special Agent John Skillestad . It says Max Kennedy , the son of Ethel and Robert , alerted the bureau in July 2006 to the letter 's pending auction at Heritage Galleries and Auctioneers Galleries in Dallas . Max Kennedy , who said he is the sole person in charge of his parents ' papers , `` stated that he had not given authority to sell , give , or donate any papers of Ethel or Robert Kennedy to anyone , '' the affidavit says . After the gallery pulled the letter from its auction , the FBI traced its provenance to Thomas Nuckols , who told authorities he had found it among the papers left by his father , Russell Thomas Nuckols , a plumber who died in 1999 . `` Thomas Nuckols said he was dumbfounded upon discovery of the letter because he had never seen it before and did not know how it came into his father 's possession , '' the affidavit says . Nuckols said he contacted the Kennedy Library in Boston , Massachusetts , but `` the person on the telephone did not seem too interested in the letter '' and referred him to a Connecticut collector , who bought it for $ 6,000 , the affidavit says . CNN has not been able to reach Nuckols . The letter was then resold to several other collectors , and was at one time valued at as much as $ 30,000 before it wound up with the Dallas auctioneer , who has cooperated with authorities , the FBI said . Last October , the FBI spoke with Ethel Kennedy , who said she remembers Russell Thomas Nuckols as a plumber who worked at the Kennedy house in Virginia during the 1960s and 1970s , the affidavit says . The 81-year-old widow of the former senator and attorney general said she `` never gave the letter to anyone to keep and under no circumstances would anyone have the authority to transfer ownership of the letter to anyone . '' The affidavit concludes that the letter `` is considered as a stolen good . '' Once the rightful owner is determined , it will be given to that person , FBI spokesman White said . `` I do n't know how long it will take . '' Jacqueline Kennedy was the widow of President John F. Kennedy , who was assassinated in 1963 . In the letter she mentions `` Stas , '' an apparent reference to Stanislas Radziwill , her brother-in-law . Jacqueline Kennedy Onassis died in 1994 . The letter is not dated , but appears to have been written shortly after Robert Kennedy died on June 6 , 1968 , the victim of an assassin 's bullet . The Dallas News printed a copy of the letter , which White confirmed is authentic . It reads : . My Ethel -- . No one in the world could have ever been like you were yesterday -- except maybe Bobby -- We are going home now -- Your phone was busy . You do n't want any more callers you must be so tired -- I stayed up till 6:30 last night just thinking -- and praying for you -- and for you in the months ahead -- . I love you so much -- . You know that anything -- Stas will take little Bobby to Africa -- I 'll take them around the world + to the moon + back -- anything to help you + them now and always -- . With my deepest deepest love . Jackie .
Stanislas Radziwill trying to determine who owns letter written by Thomas Nuckols in 1999 . Letter passed from collector to collector , but widow says she gave it to no one . Letter found among papers of Jackie Kennedy , who died in 1999 , son says . Son Russell Nuckols told authorities he found it among the papers left by his father .