About two weeks ago, Arshad Mahmood, a cabdriver in Prince George's County, celebrated the fact that he had legalized his status in the United States.

With his new immigration status, Mahmood, 45, dreamed of filing paperwork to bring his wife to the United States from Pakistan, said Carl Sehuettler, general manager of Silver Cab Co. in Lanham, which shared a dispatch center with Mahmood's Checker Cab Co.

Mahmood and his dream died on an Oxon Hill street early yesterday or late Thursday, authorities said.

About 1:15 a.m. yesterday, a Prince George's police officer on routine patrol found Mahmood slumped over the wheel of his black-and-white checked taxi in the 4600 block of Winterberry Lane, officials said. The taxi's engine was running.

Mahmood was dead of a gunshot wound to the upper body, officials said.

Police said they knew of no motive or suspects in the case. Given the circumstances, police said, they were investigating the possibility Mahmood was slain during a robbery.

"We're definitely looking for witnesses to come forward," said Officer Debbie Carlson, a police spokeswoman. Carlson urged anyone who might know anything about the attack to call Prince George's police.

Sehuettler said Mahmood was dispatched about 11 p.m. Thursday to pick up a fare from the Southern Avenue Metro station, on the District-Prince George's border. The call for a cab came from a pay phone at the Metro station, Sehuettler said.

Mahmood never returned from the assignment, Sehuettler said.

Sehuettler said he believed that Mahmood had a teenage son who lived with him, but he said he did not know much about Mahmood's personal life. Police said Mahmood lived in Alexandria.

Mahmood was well liked by other cabbies, Sehuettler said.

"All the cabbies have been talking about [the killing] all day," Sehuettler said. "He was a nice guy. He'd come in laughing and joking."

Including Mahmood, at least seven cabdrivers have been killed in Prince George's since 2000.

Driving a cab is one of the most perilous jobs in the country. One federal study found that cabdrivers were four times as likely as police officers to be killed.

In 2001, Prince George's County Council member Thomas R. Hendershot (D-New Carrollton) proposed equipping the approximately 775 taxis licensed in the county with digital security cameras. Advocates for the cameras said they are effective crime deterrents.

But some cabbies opposed the idea, saying installing cameras would be an invasion of privacy, said John A. Lally, an attorney for the cab industry in Prince George's. The camera proposal stalled and died.

"People think cabdrivers are mobile ATMs," Sehuettler said. "The truth is, they don't carry much money."

He said most cabdrivers carry less than $100, just enough to make change.

Staff researcher Meg Smith contributed to this report.