Allison Guerriero, the former mistress whose evidence helped convict jailed FBI counterintelligence chief Charles McGonigal, has died suddenly in Florida, with text messages seen by the Daily Mail revealing she had feared Russian reprisals before her death. The 52-year-old, who spent 18 months in a relationship with McGonigal that ultimately exposed his covert work for Russian oligarch Oleg Deripaska, died at her Boynton Beach apartment on Thursday evening, hours after posting dozens of messages on X attacking the FBI. Her death matters because it raises unanswered questions about whether foul play was involved, given her role in bringing down a senior US intelligence official with Kremlin links, and because police have withheld records citing an active criminal investigation.

Guerriero told researcher Anthony Gonzales in texts that she had "concerns" about retaliation but insisted "they don't scare me," adding that if Russian operatives had wanted her dead she "would be dead five or six years ago." No cause of death has been made public, and her father, Bill, 80, confirmed only that she died suddenly; a Daily Mail public records request to Boynton Beach police was refused under a Florida statute exempting active criminal investigation material. Her death came a day after security consultant Jackie Singh published a critical article about her, and Singh told the Daily Mail she doubted Guerriero was "whacked" but suspected she may have been destabilised by the piece, raising the possibility of suicide. McGonigal, 58, is currently serving a 6.5-year prison sentence.