As his sister Victoria Gotti began a book tour befitting a celebrity author, John "Junior" Gotti sat in court, portrayed as a merciless killer by federal prosecutors who want to show he was far different from his entrepreneurial sister.

Last week, the government used its star witness — childhood friend John Alite — to convince a Manhattan jury that Gotti was as lethal a threat to society as anyone else in the Gambino crime family once led by his late father, John Gotti Sr.

The testimony marked the first time in four racketeering trials for Gotti over the last four years that the government had produced a witness who could so dramatically link Gotti to stabbings, murders and beatings in the 1980s and 1990s.

Prosecutors seem intent on taking a shine off the Gotti name that has resulted in part from his sister, who was on the "Growing Up Gotti" TV reality show and whose book, "This Family of Mine," was published with a publicity blitz as her brother's trial began last month.

Gotti's defense attorney, Charles Carnesi, says Gotti quit the Gambino family in 1999 when he pleaded guilty to federal charges and began serving a five-year prison sentence. He also says Gotti had nothing to do with killings.

Gotti, 45, seemed unflappable through his trials until Thursday, when a U.S. marshal told a prosecutor that he saw him mouth the words: "I'll kill you" to Alite. When Alite responded, Gotti erupted, shouting: "You're a punk! You're a dog! You're a dog! You always were a dog your whole life, you punk dog."

Through Alite, prosecutors have portrayed Gotti as a bully with a fragile ego, someone who Alite said once stabbed a happy-go-lucky Irish friend for making fun of him during a shot-drinking game after he went to the bathroom to vomit.

"It was his ego. ... John hates losing," Alite said.

He said Gotti shot another acquaintance who made fun of his small handgun.

"Is this big enough?" Alite quoted Gotti as saying as he grabbed a nearby rifle and shot the man in the hip.

Alite said Gotti repeatedly urged him to earn his organized crime credentials by killing Georgie Grosso, a childhood friend of Alite who was telling people that he was selling drugs for John Gotti.

"John Gotti Jr. kept saying to me in '88: `You didn't kill this kid yet, you didn't shoot him, you didn't do this.' ... He wanted me to kill him," Alite said.

"I wanted to prove I was capable of killing guys and hurting guys and I was capable of being like everybody else that's tough guys in the mob, capable of doing work, which is a big thing in the mob for respect," Alite testified.

Alite said he eventually carried out the killing after spending an evening watching football with his victim to "rock him to sleep," a mob term used to explain the practice of making sure the victim does not know he is about to be attacked.

He said he shot Grosso in the back of the head in a car before dumping his body in some brush along a road to comply with Gotti's instruction that he not hide the body so the message gets out that death is the penalty for tying the Gotti name to drugs.

Alite, a 47-year-old muscular man who was born in Queens, said he was introduced to organized crime at age 6 when his uncle took him to a Bronx gambling den with a member of the Gambino family. He said men there gave him $20, $50 and $100 bills.

He said organized crime was like joining the Army.

"It was something to be proud of, especially in my neighborhood. So being around gangsters was like somebody like yourselves would think as being a CEO of a company," he told a prosecutor as he testified.

Alite said he was enrolled at the University of Tampa with a baseball scholarship but dropped out after a semester because he needed major arm surgery that spoiled his baseball career.

He said Gotti "brought me up on understanding the life and the protocol of it," including such things as each family member being greeted in the order of their rank and a requirement that nobody put a fork in their food at dinner until Gotti had done so.

He said his disenchantment with mob life began when Victoria Gotti's then-husband threatened him after Alite warned he would tell John Gotti Sr. if he continued abusing her. He said John Gotti Jr. disallowed retribution because it involved his brother-in-law.

"I understood the mob. I understood it's blood. I'm not blood. I'm just another guy that he used to hurt people," Alite said.