CHICAGO (Reuters) - Every two weeks, Cynthia Lewis contacts the detectives investigating the homicide of her brother on Chicago’s south side almost a year ago.

Tyjuan Lewis is pictured in this undated handout photo, along with his sister Cynthia Lewis (top photo). Cynthia Lewis/Handout via REUTERS

They have had no success finding who shot Tyjuan Lewis, a 43-year-old father of 15, near his home in the quiet Roseland neighborhood of single-family houses.

The death of Lewis, who delivered the U.S. mail for 20 years, is one of hundreds of slayings in 2015 that have gone unsolved as the number of homicides soared in Chicago, piling pressure on a shrinking detective force.

In a city with as many as 90 shootings a week, homicides this year are on track to hit their highest level since 1997.

Chicago’s murder clearance rate, a measurement of solved and closed cases, is one of the country’s lowest, another sign of problems besetting police in the third biggest city in the United States.

Over the past 10 years Chicago has consistently had one of the lowest clearance rates of any of the country’s 10 biggest cities, according to data from the Federal Bureau of Investigation and the Chicago Police Department.

Last year, Chicago police had 480 murder cases and solved 223 murders that had been committed in 2015 or before, for a clearance rate of 46 percent, according to Chicago police figures.

That is well below the average national rate of 63 percent, and the average rate of 68 percent for cities with populations of more than 1 million in the past decade, according to FBI figures.

Chicago, with a population of 2.7 million, has more shootings and homicides than any other U.S. city, according to FBI and Chicago police data, and more shootings by law enforcement than other major cities, according to police department figures on officer-involved shootings compiled by Reuters. Its police department is under federal investigation for the use of lethal force by its officers.

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Detectives and policing experts interviewed this week said Chicago struggles to solve murders because of declining numbers of detectives, the high number of cases per detective and because witnesses mistrust the police and fear retaliation from gangs.

DETECTIVES OVERWHELMED

The number of detectives on the Chicago police force has dropped to 922 from 1,252 in 2008. One detective who retired two months ago said investigators are overwhelmed. Not all of the detectives are assigned exclusively to homicide cases.

“You get so many cases you could not do an honest investigation on three-quarters of them,” he said in an interview. “The guys ... are trying to investigate one homicide and they are sent out the next day on a brand new homicide or a double.”

A tight budget and focus on putting more police on street patrol has contributed to the shrinking detective force. Because police departments are not all structured the same, it can be difficult to compare numbers. But Chicago has proportionally fewer detectives than other U.S. cities, according to data on some of the country’s biggest police forces.

About 8 percent of Chicago’s roughly 12,000 police are detectives. In New York City, which has a police department of 34,450, 15 percent are detectives. In Los Angeles, which has a police department of 9,800 sworn officers, 15 percent are detectives.

John DeCarlo, professor of criminal justice at the University of New Haven in Connecticut, said better salaries also attract police talent from around the country and may be one of the factors that has helped drive higher clearance rates in cities like Los Angeles and San Diego.

FRAYED RELATIONS

Chief of Detectives Eugene Roy, who is due to retire soon, said to solve more murders the department was working with other law enforcement agencies, better using technology such as portable gunshot residue testing kits and increasing training for detectives on the use of surveillance video.

“The Chicago Police Department is taking the steps necessary to increase the number of detectives while also making available greater resources for existing detectives to do their jobs more effectively,” Roy said in an emailed response to questions from Reuters.

Roy said the department was also working to restore public trust in the police. A task force set up by Mayor Rahm Emanuel found earlier this year that the police department was not doing enough to combat racial bias among officers or to protect the rights of residents.

Craig Futterman, a law professor at the University of Chicago, said frayed relations between police and minority communities were not unique to Chicago. “But it’s of a different grade here,” Futterman said. “It’s incredibly difficult to solve violent crime if people won’t talk to you.”

Another detective who retired this year said an even bigger problem was the fear of gangs.

“People see homicides but they are afraid to get involved,” he said. “Detectives are out on an island. No one wants to help them.”

According to Chicago police data, 61 percent of homicides last year were gang related, the highest proportion for at least 10 years. Intelligence-gathering can be difficult because the city’s gangs tend to be fragmented.

Lewis, the mailman, was not in a gang and lived in a neighborhood where residents complain more about abandoned houses than gangs. “I hate to try and make his (case) sound different, but it is,” said Cynthia Lewis, 41.

His family is convinced he was killed by someone he knew and frustrated that police have not found even a suspect.