Sven-Erik Alhem, a former chief prosecutor in Sweden, said prosecutor Marianne Ny "should have made sure Assange was able to give his version of events in detail."
Assange's lawyers say prosecutors have rebuffed his offer to be questioned from London about rape and sexual misconduct claims by two Swedish women. The head of the secret-spilling website denies wrongdoing.
Special Report: WikiLeaks
Alhem, a defense witness, also said it was "extraordinary" that a prosecutor had leaked Assange's name to the media.
CBS News producer Steve Berriman says Alhem also questioned the prosecution's choice of words in referring to Assange as "the accused."
"In my view the word accused does not correspond with the Swedish word "suspect", he said, saying Assange should have been referred to as a "suspect."
Assange's lawyers claim publicity about the case and the Swedish custom of hearing rape cases behind closed doors mean he would not get a fair trial if he is sent to Sweden. His attorney, Geoffrey Robertson, that closed-door hearings would be "a flagrant denial of justice.
But the British lawyer representing Sweden, Clare Montgomery, countered that Swedish trials were based on the principle that everyone deserves "a fair and public hearing." Evidence is heard in private in some cases, but it will often be published after the trial and recited in the judgment.
Montgomery said Ny had issued an arrest warrant for Assange only after making repeated unsuccessful attempts to arrange an interview with him.
In a court document read aloud by Montgomery, Ny said that "it must have been crystal clear to Julian Assange ... that we were extremely anxious to interview him."
But, Ny said, an interview could not be set up and at one point Assange's Swedish lawyer was unable to contact him for several days. Ny said given this background, "We consider Julian Assange is an obvious flight risk and it cannot be considered an overreaction to detain him."
Assange's wide-ranging arguments against extradition range from criticism of Ny to claims that he could eventually be extradited from Sweden to the United States, and even sent to the detention center at the U.S. Navy base in Guantanamo Bay, Cuba.
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The 39-year-old Australian, wearing a blue suit, sat in the dock at London's Belmarsh Magistrates' Court on the second day of a two-day hearing.
The secrets-spilling website touched off an international uproar when it released secret helicopter video showing a U.S. attack that killed two Reuters journalists in Iraq. It later began publishing classified U.S. diplomatic cables whose revelations angered and embarrassed the U.S. and its allies.
American officials are trying to build a criminal case against WikiLeaks. Assange's lawyers claim the Swedish prosecution is linked to the leaks and politically motivated.
Assange was arrested in London in December after Sweden issued a warrant on rape and molestation accusations.
He was released on bail on condition that he live - under curfew and electronically tagged - at a supporter's country mansion in eastern England, and Assange has managed to conduct multiple media interviews and sign a reported $1.5 million deal for a memoir.
The extradition hearing is due to end Tuesday, but Judge Howard Riddle could take several weeks to consider his ruling - which can be appealed by either side.