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Former Major League Baseball player Barry Bonds goes through a security screening as he arrives for the first day of his perjury trial on March 21, 2011 in San Francisco

Kimberly Bell – who was Barry Bonds' girlfriend for nine years – gave graphic and dramatic testimony today about changes to the slugger's body and moods, allegedly from taking steroids. 

Bell was softly sobbing, the Mercury News reported, as she told the jury about Bonds' troubling transformation from 1999 to 2003, the same time period that Bonds' slugging prowess reached its peak. By the end of their relationship Bonds told her he would "cut my head off and throw me in a ditch," and that he would "cut out my breast implants because he paid for them," the Merc reported. 

Bell, now 41, is a key witness in the government's case against Bonds for allegedly lying to a grand jury about his steroid use.

She told the jury she observed changes in his body, including acne, growth of hair on the chest and shrinkage of the testicles, as well as increased irritability in the same time period.

"He was just increasingly aggressive, irritable, agitated," Bell said under questioning from prosecutor Jeff Nedrow in the court of U.S. District Judge Susan Illston.

Bell said that Bonds told her in either 1999 or 2000 that he was taking steroids after she asked him about an elbow injury.

Under nearly five hours of cross-examination by defense attorney Cristina Arguedas, Bell denied that she was bitter and seeking revenge against Bonds because he married another woman in 1998, relegated her to being a "road-trip girlfriend," and then broke up with her in 2003.

Arguedas asked whether Bell had been in "an absolute fury" when she learned through her lawyer in 2004 that Bonds was refusing to pay the remainder due on a house he helped her buy in Scottsdale, Ariz.

"I was hurt by his action," Bell answered. "Angry? No."

Bell also denied Arguedas' suggestions that she sought to embarrass Bonds and create publicity that would enable her to make money from a future book when she appeared on numerous radio and television shows and had an interview in Playboy Magazine. 

"Is it not the case you have taken many opportunities to disparage Mr. Bonds in many ways and in the most vulgar ways possible?" Arguedas asked.

"No, I was asked questions and I answered them," Bell answered.

The book, for which Bell was considering the titles "In the Shadow of a Giant" or "Giant Mistake," was never written, she said.

Tomorrow's witnesses will include three baseball players: Colorado Rockies' and former Oakland A's first baseman Jason Giambi and former major league players Jeremy Giambi and Randy Velarde.

They are expected to testify that Bonds' trainer, Greg Anderson, gave them performance-enhancing drugs along with instructions and schedules for using them, according to pretrial prosecution filings.

Bonds admitted during his grand jury testimony to taking substances known as "the clear" and "the cream" that prosecutors say were designer steroids, but said he believed they were merely flaxseed oil and an arthritis cream, his lawyers have said.