John McAfee had a suicide note in his pocket when he was found dead in his prison cell in Spain last week.
McAfee's death came hours after a court ruled he would be extradited to the U.S. to face federal charges of income tax evasion and wire fraud.
The note was found after the 75-year-old software designer hanged himself in his cell in Barcelona on Wednesday.
However, his widow Janice McAfee said her husband was not suicidal and would not have taken his own life.
Janice McAfee, 38, is demanding a "thorough investigation" into his death, saying her husband did not appear suicidal when they last spoke.
"His last words to me were: 'I love you and I will call you in the evening', those words are not words of someone who is suicidal," she told reporters.
She fought back tears as she spoke with reporters outside the walls of the Brians 2 penitentiary northwest of Barcelona where she recovered her late husband's belongings.
"I don't believe he did this, I will get answers," she said.
McAfee also confirmed he wasn't suicidal in a tweet last year.
"I am content in here. I have friends. The food is good. All is well. Know that if I hang myself, a la Epstein, it will be no fault of mine," McAfee tweeted on October 15.
Janice, a former prostitute, met John in Miami after he solicited her services in 2012. They got married the following year.
John McAfee was arrested at the Barcelona airport in October 2020 on an outstanding warrant issued by prosecutors in Tennessee.
Prosecutors were seeking up to three decades of imprisonment for allegedly evading more than $4 million in taxes.
McAfee is best known for designing the award-winning antivirus software that was used by 80% of Fortune 100 companies worldwide. He later sold the rights to Intel for $100 million.