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(USA Today) -- Acclaimed champion and accused cheat, Lance Armstrong still hasn't distanced himself from all those chasing after him.

The seven-time Tour de France winner who in February saw a two-year federal investigation into his alleged use of performance-enhancing drugs dropped without charges being filed, is back in the spotlight of doping suspicions.

The U.S. Anti-Doping Agency has accused Armstrong and five former members of his support staff - three doctors, a trainer and a team manager - of engaging in a massive doping conspiracy from 1998 to 2011. Armstrong, 40, who retired from cycling last year, could see his Tour titles get stripped as a result.

USADA's letter to Armstrong dated June 12 includes previously unpublicized allegations against him, saying blood samples taken in 2009 and 2010 were "consistent with blood manipulation including EPO use and/or blood transfusions."

But they are not positive tests. As it did with disgraced Olympic champion sprinter Marion Jones, USADA has built a non-analytical case, based on evidence such as testimony.

The letter, first reported by The Washington Post, says riders with firsthand knowledge will testify that Armstrong used EPO, blood transfusions and testosterone and that he administered them to other cyclists from 1998 to 2005. Witnesses also will testify, the letter says, that Armstrong used human growth hormone before 1996.

Armstrong fired back with a defiant denial of the charges, as has become his custom. In a statement Wednesday posted on Twitter, he said, "These charges are baseless, motivated by spite and advanced through testimony bought and paid for by promises of anonymity and immunity."

He repeated his denial of doping and said he has passed more than 500 drug tests and never failed.

The USADA, which oversees anti-doping in U.S. Olympic sports, can issue bans but cannot bring criminal charges. It will forward the case to a review board, which recommends whether to proceed with a hearing before an arbitration panel.

The letter to Armstrong says that if a hearing is held, it should take place by Nov. 1 but could occur before then, a person familiar with the case told USA TODAY Sports on the condition of anonymity because the letter was not released.

Travis Tygart, CEO of USADA, would not comment but said in a statement that it is the agency's duty "to fairly and thoroughly evaluate all the evidence available and when there is credible evidence of doping, take action."

David Howman, director general of the World Anti-Doping Agency, declined to assess the strength of the evidence but told USA TODAY Sports, "I think it's significant that it's not an athlete alone being charged. It's an athlete/entourage. I think the charge is significant."

When asked about non-analytical cases and the fact that Armstrong hasn't tested positive, Howman pointed to the sanctions against Jones. "There have been a lot of athletes who have faced sanctions through non-analytical evidence," Howman said. "We do not rely on science only nowadays. You cannot accept that science alone will find those who might be breaching the rules. So this is not unusual. It's something that's becoming more normal and accepted."

The USADA's letter and an earlier letter from one of Armstrong's attorneys details the level of animosity that exists - and has for years - between the two.

The USADA letter alleges that Armstrong's team engaged in an organized conspiracy to conceal and cover up doping conduct dating to 1999. It says it has witnesses who will testify that "Lance Armstrong and other co-conspirators engaged in activities to conceal their conduct and mislead anti-doping authorities including ... attempts to intimidate, discredit, silence and retaliate against witnesses."

Last week, Armstrong's attorney, Robert Luskin, sent a letter to USADA declining the agency's invitation to meet with Armstrong to discuss the allegations in person.

The June 8 letter, a copy of which was obtained by USA TODAY Sports, accuses the USADA of conducting not an investigation but "a vendetta, which has nothing to do with learning the truth and everything to do with settling a score and garnering publicity at Lance's expense."

As part of the process set into motion by the USADA's letter, Armstrong is banned from competing in triathlon, a sport that he focused on after retiring from cycling competition.