(CNN) A student working on his doctorate at a New York university was found dead by his roommate earlier this month five hours after the student made an "unintelligible" 911 call for help, according to a police official.

First responders couldn't find Yeming Shen because his 911 call February 10 was not understandable and it was made on his foreign-issued cell phone that was only traceable to an area -- not a specific address -- in the city of Troy with several apartment buildings, Capt. Steven Barker said Friday.

Officers and firefighters went around knocking on doors at the apartments near Rensselaer Polytechnic Institute, but couldn't find the man, who called 911 at 11 a.m., he said.

Around 5:45 p.m., Shen's roommate returned to their apartment, found him dead, and called 911, Barker said. A preliminary autopsy determined he died of influenza, Richard Crist, director of operations for Rensselaer County, said earlier this month.

"The incident draws to attention the severity of the flu and the devastating effects it can have," Barker said. "We continue to extend our thoughts to the family and friends of Mr. Shen, as well as the responders involved throughout the incident."

An internal investigation determined authorities took appropriate actions, and even went beyond normal expectations, he said.

The problem in tracing the 911 call was Shen used a cell phone from China and a Chinese carrier that let him use a phone number with a local area code that was not linked with a local address, Barker said. Calls were routed to his Chinese number, but the 911 dispatcher could only see the local number.

Checks with cell phone providers and apartment management to get an address associated with the New York number came up empty, he added.

The 911 dispatcher was unable to understand Shen, Barker said.

"The sounds were unintelligible. This could be due to a potential language barrier, Mr. Shen's flu symptoms, or both," he said. Shen, who had lived in China, had been in the United States for more than a year, he told CNN.

According to the university, Shen was working on his doctorate in decision sciences and engineering systems with a focus on interdicting interdependent networks. He earned his master's degree in operational research and cybernetics and his bachelor's degree in mathematics from Sun Yat-Sen University in Guangzhou, China, the university said.

"Our thoughts and prayers are with Yeming's family, fellow students, friends, and teachers. We are all saddened by the loss of one of our own. Please support each other during this difficult time," school President Shirley Ann Jackson said in an email to students and faculty.

One of Shen's professors, Thomas Sharkey, wrote in the university newspaper that Shen was using "his tremendous mathematical mind" to create new methods of disrupting transnational criminal networks.

"Simply put, I believe that the legacy of his research is that it will make the world a better place," Sharkey wrote.

The 2019-2020 flu season, which began September 29, is projected to be one of the worst in a decade, according to the National Institute of Allergy and Infectious Diseases.

At least 29 million people in the US have gotten the flu and at least 16,000 people have died from it, the US Centers for Disease Control and Prevention reported.