By Scott Malone and Elizabeth Barber

BOSTON (Reuters) - Accused Boston Marathon bomber Dzhokhar Tsarnaev told a high school friend his older brother was "very strict" and might not like him because he was not Muslim, the friend testified on Tuesday.

Tsarnaev, 21, is charged with killing three people and injuring 264 with a pair of homemade pressure-cooker bombs at the race's crowded finish line on April 15, 2013, and shooting dead a university police officer three days later.

Stephen Silva, who federal prosecutors contend loaned Tsarnaev the gun used in the shooting, said he had long been friends with the defendant but had never met his 26-year-old brother, Tamerlan, who died following a gunfight with police four days after the bombing.

"He said his brother was very strict, very opinionated, and that since I wasn't a Muslim he might give me a little shit for that," Silva said.

Defense lawyers opened the trial at U.S. District Court in Boston with the blunt admission that Dzhokhar Tsarnaev had carried out the crimes he is charged with, focusing their hopes on the jury sentencing him to life in prison rather than the death penalty he could face if found guilty.

They contend Tamerlan was the driving force behind the attacks and that his younger sibling followed out of subservience.

Prosecutors called Silva, 21, to the witness stand to discuss the loan of the rusty Ruger P95 handgun they contend was used to shoot dead Massachusetts Institute of Technology police officer Sean Collier on April 18, 2013.

Silva has pleaded guilty to federal gun and drug charges, but was offered leniency in exchange for his testimony. He testified he had gotten the gun from a friend, intending to use it to protect his drug business, and also used it in a robbery.

Tsarnaev asked to borrow it, saying he too was interested in committing a robbery, Silva testified.

In the most aggressive cross-examination by the defense in eight days of testimony, Silva acknowledged having posted on Facebook and having told the Federal Bureau of Investigation that he believed the bombing must have been Tamerlan's idea.

"At the time that's what I felt, yes," Silva said in response to questioning by defense attorney Miriam Conrad.

He also acknowledged having told prosecutors in August he used "peer pressure" to persuade Dzhokhar to smoke marijuana, which Silva sold.

"That's what I said but I stated it wrong," Silva said on Tuesday.

Silva also testified that Dzhokhar Tsarnaev had once called him a "kafir," an Arabic word meaning non-believer or infidel, in response to Silva calling the defendant a "Russian refugee".

Tsarnaev is an ethnic Chechen whose family moved to the United States a decade before the attack.

Other than the "kafir" incident, Silva said Tsarnaev had rarely talked about religion.

FINDING TSARNAEV

Also on Tuesday, the owner of the boat where Tsarnaev hid after a gunfight with police recalled stepping into his backyard after a day-long lockdown was lifted and finding a person in his watercraft.

David Henneberry described waking up the morning after a gunfight between the Tsarnaev brothers and police rocked his suburban neighborhood and noticing something wrong about the winter covering of his boat, but presuming it had been blown around by the wind.

He put off checking it until after authorities had lifted a shelter-in-place order on Boston-area residents four days after the bombing.

"I went to check on the boat and basically see why the strap was loose and I noticed a lot of blood," Henneberry said. "I just kept fixating on this blood and then, I just, my eyes looked at the other side of the boat and that's when I saw a body in the boat ... I got off the ladder pretty quick and went in the house."

When prosecutors wrap up their case it will be the defense's turn to call witnesses, who could include Tsarnaev. After that, the jury will consider Tsarnaev's guilt. If he is found guilty, a second phase will play out that will focus on sentencing.

The bombing killed restaurant manager Krystle Campbell, 29, graduate student Lingzi Lu, 23, and 8-year-old Martin Richard.

Henneberry said after he called 911, bringing dozens of heavily armed police who fired scores of rounds into the boat where Tsarnaev was discovered.

The jury also saw two wooden slats from the boat into which a message had been carved which read: "Stop killing our innocent people and we will stop."

(Reporting by Scott Malone; Editing by James Dalgleish)