By Elizabeth Barber

BOSTON (Reuters) - Testimony was suspended on Thursday in the sentencing phase of convicted Boston Marathon bomber Dzhokhar Tsarnaev's trial due to a juror’s illness, a federal judge said.

The trial will resume on Monday once one of the 12 jurors and six alternate jurors hearing the case recovers, Judge George O’Toole told the court.

The jury found the 21-year-old ethnic Chechen guilty this month of bombing the world renowned race on April 15, 2015. It is now tasked with deciding whether he should be sentenced to death or life in prison.

Court is expected to open with prosecutors cross-examining Alexa Guevara, a 21-year-old college friend of Tsarnaev's who sobbed as she told jurors on Wednesday that he was a kind person who encouraged her to go to art school, liked joking around, and was more decent than other college guys. Court officials said some of Tsarnaev's relatives may also testify on Monday.

Lawyers seeking to spare Tsarnaev the death penalty have sought to portray him as a bright young man whose chance at a good life in the United States was derailed when he fell under the influence of his now-dead older brother Tamerlan.

The explosions at the marathon's crowded finish line killed three people and injured another 264, many of whom lost limbs in the blasts. It marked the worst terror attack on U.S. soil since Sept. 11, 2001.

Tamerlan Tsarnaev, an accomplished boxer who became fascinated with militant Islam after a trip to Russia's Dagestan region, was killed days after the bombing following a shootout with police.

Prosecutors pursuing a death sentence contend that Dzhokhar Tsarnaev was an equal partner to his brother in the bombings. They have said Tsarnaev lived a double life, pretending to be a typical college student while secretly watching al Qaeda propaganda online and preparing to bomb the race.

Martin Richard, 8, Chinese exchange student Lu Lingzi, 23, and restaurant manager Krystle Campbell, 29, died in the bombing. The Tsarnaev brothers shot dead Massachusetts Institute of Technology police officer Sean Collier three days later.

Richard's parents and Collier's sister have urged prosecutors to drop their pursuit of a capital sentence.

(Editing by Richard Valdmanis and David Gregorio)