Why was the case of Armstrong closed?

The case against Lance Armstrong connected with doping is proclaimed to be closed. This athlete remains to be considered a 7-time winner at Tour de France.
It is known that federal prosecutors tried to define whether this racing cyclist and his teammates have taken part in a doping program. The duration of the investigation has been approximately 2 years.
Lance Armstrong denied that he has used controlled substances. The accusations against this cyclist threatened to his athletic career as well as to his Foundation of cancer research and support. The efforts to prove that this athlete used steroids were in vain.
Lance Armstrong said that he had heard that the US Attorney’s Office decided to close the investigation. He confirmed that it was a right decision. Armstrong claimed that he was waiting to continue his usual life, being a father, a competitor and an advocate in the fight against cancer.
Andre Birote, an attorney proclaimed during a press conference that the US Attorney’s Office closed the investigation linked with the case of Lance Armstrong. This attorney didn’t notice about any reason of this decision. But he just said that previous similar investigations were also closed.
For example, the investigation linked with Barry Bonds was claimed to be unsuccessful. Prosecutors couldn’t prove that this athlete had cheated about intake of steroids. As for the case connected with Roger Clemens, the trial was indicated for another time because the judge announced about previous mistrial.
Investigators believed that a doping program was organized by Armstrong’s team. They wanted to determine whether it was so as they believed. Authorities investigated whether Armstrong encouraged or induced doping.
In fact, prosecutors put efforts to find out whether Armstrong and his team broke federal conspiracy and fraud charges. While Barry Bonds testified before a federal grand jury and Clemens testified before Congress, Lance Armstrong wasn’t required to present before a grand jury. Barry Bonds and Clemens were accused in lying under oath.
 The former Armstrong’s teammate Frank and her wife Betsy Andreu charged Armstrong with usage of banned drugs. They claimed that they were shocked by the decision to close the case. They concluded that such situations happened due to possessing money and corruption.