SAN DIEGO — In a bid to save David Westerfield from death row, his defense Thursday morning called a string of witnesses who recalled the convicted killer as a once successful engineer who designed several life-enhancing medical products.

"He was a very talented guy," said Carmine Genovese, an engineer who worked with Westerfield for 20 years and winked at the defendant as he took the stand.

The six men and six women of the jury, who will decide whether Westerfield gets a life sentence or death for the murder of Danielle van Dam, took occasional notes as other engineers and a physician described Westerfield's designs, which include prosthetic knuckle implants and a rehabilitation device for knee injuries.

Carmen Genovese described Westerfield as a "very talented guy."

"I would guess it's been used by millions," said orthopedic surgeon Richard Coutts, who conceived the knee device and worked with Westerfield to develop it.

Defense lawyer, Steven Feldman, told jurors Wednesday that in spite of the killing, Westerfield left a "footprint" of good during his 50 years. His grown children, Neal and Lisa, are expected to take the stand later in the penalty phase, describe their home life and beg the jury to spare their father.

Before his arrest for the February kidnapping and murder of 7-year-old Danielle, Westerfield owned his own engineering business, the culmination of two decades of work in the design industry.

Westerfield was awarded patents for the knee device, the implants and a pulley system for a product to increase shoulder flexibility. The "shoulder flexer" became a best-selling product with more than 600,000 users, according to Judy Ray, the owner of a manufacturing company that hired Westerfield for the project.

Westerfield also designed an airport security device currently used in San Francisco that allows airline employees to quietly flag luggage for screening with special tags, Genovese said.

"This particular product was very revolutionary for its time," said Genovese.

Ron Lawrence testified for Westerfield Thursday.

In his cross-examination, prosecutor Jeff Dusek suggested the defense was overstating Westerfield's role in the inventions and his desire to help others. Ron Lawrence, a friend and former co-worker of Westerfield, acknowledged that the defendant, who never earned a bachelor's degree in engineering, acted only at the direction of more experienced, well-educated engineers.

When Lawrence said an underwater surveillance vehicle that Westerfield helped design in the late 1970s saved lives of divers, Dusek asked, "Did he invent any of these things?"

"No," Lawrence acknowledged.

"He was getting paid this whole time?" Dusek asked.

"Yes," Lawrence said.