Dr. Tanya Holzmayer, a pioneering scientist, was surprised Wednesday night to find a Domino's Pizza deliveryman at the front door of her Mountain View home.

Moments later, a former colleague appeared out of the dark, shot her dead and ran off, police said.

Guyang ``Matthew'' Huang called his wife in Foster City with the news: I just killed my ex-boss. Now I'm going to kill myself.

Within an hour, a jogger found Huang's body off a path near the San Mateo Bridge. A cell phone was in Huang's pocket and a .380-caliber handgun lay near his hand.

Investigators on Thursday were just beginning to put together the details of the deadly nexus between the two immigrant scientists.

``It looked like an ambush,'' said Mountain View Police spokesman Jim Bennett. ``He may have used the pizza to lure her out.''

A former colleague of both Holzmayer and Huang thinks he knows the motive: Holzmayer fired Huang from his job at PPD Discovery, a biotech company in Menlo Park, according to Dr. Igor B. Roninson.

``She told me she got orders from senior management to fire him,'' said Roninson, a genomic scientist with the University of Illinois-Chicago and a consultant for PPD. ``She had to fulfill those orders, but was very upset. She had no choice, no options.

``But this is a year later!''

A company spokeswoman said Huang left PPD in June, but she wouldn't confirm that he was fired. Neither Huang nor Holzmayer were still with the company. Holzmayer had quit in December to start her own biotech venture.

Both Holzmayer, 46, and Huang, 38, were highly regarded in genetics.

She was a Russian-born genomic scientist who had co-invented a tool that has helped find hundreds of molecular targets to combat cancer and HIV. He was a brilliant scholar -- scoring 11th out of 230,000 students on his college entrance exams in China -- and an activist who fought for reform in his homeland once he came to the United States to study in 1986.

Outside of the company's Menlo Park office on Thursday, puffy-eyed employees gathered in small groups but shook their heads when approached by a reporter.

On Wednesday, just past 8:30 p.m., the Domino's deliveryman had pulled up to Holzmayer's home on Windmill Park Lane. Holzmayer and her teenage son were inside when the doorbell rang. She told the deliveryman that she hadn't ordered a pizza, according to Mountain View police.

Huang appeared from behind the deliveryman. He shot Holzmayer several times at close range in the chest and head, police said. As Holzmayer fell in her doorway, Huang ran to a Ford Explorer and drove away.

Police said the deliveryman witnessed the shooting but was not involved. A Domino's spokeswoman said the driver wasn't hurt, but would be offered counseling and time off.

Just a few doors away, the Brogan family heard the shots, then the tires screeching, and saw the deliveryman running in a panic. After calling 911, Evan Brogan went with his mother, Micheline, a nurse, to their neighbors' home. Holzmayer was lying in her doorway with no pulse.

``We were just trying to help. But she was gone,'' Evan said.

Less than an hour after the shooting, Huang called his wife, according to Foster City Police Capt. Craig Courtin. He told her about the shooting and that he was going to kill himself, police said. He told her he was near their home by the bay. Then he hung up.

Huang's wife called 911, and Foster City police used search dogs to comb the area. They ran into a jogger who had seen Huang's body lying off the walkway that locals call ``The Levee.'' He had fired a single bullet into his head, according to Robert Foucrault, San Mateo County's acting coroner.

Soon afterward, police interviewed Huang's wife, whom they wouldn't identify. She said she believed that her husband had killed Holzmayer and told them where they both had worked.

People who answered the door Thursday at Huang's apartment declined any comment.

Holzmayer and her family came to the United States in 1989, according to Roninson, a classmate of hers at Moscow State University in Russia.

She was an intellectual, he said, torn between becoming a classical pianist or a scientist. She chose genomics over her beloved Chopin, focusing on helping create new drugs that interfere with replication of the virus that causes AIDS.

Until December, Holzmayer had served a four-year tenure as senior vice president of genomics for PPD Discovery, a division of PPD Inc. of Wilmington, N.C. It was at PPD Discovery that Holzmayer met Huang, who began working as the firm's director of molecular biology and bioinformatics in early 2000.

Roninson said Huang ``gave a perfectly normal, charismatic impression.''

Holzmayer told Roninson two weeks ago that she had just received funding for her new start-up venture to use modern methodologies to develop new drugs.

``She said she had never felt so happy in her life.''