Every two weeks, Cynthia Lewis contacts the detectives investigating the homicide of her brother on Chicago's south side almost a year ago.

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.

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Tyjuan Lewis, a 43-year-old father, was shot near his home in the quiet Roseland neighborhood last year. He is pictured above in an undated photo with his sister, Cynthia

Cynthia Lewis (pictured) is still looking to get the case involving the murder of her brother, Tyjuan, solved

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 per cent, according to Chicago police figures.

That is well below the average national rate of 63 per cent, and the average rate of 68 per cent for cities with populations of more than one 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.

The death of Lewis (pictured), 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

It also has 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.

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.

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 eight per cent of Chicago's roughly 12,000 police are detectives.

In this July 5, 2016 photo, family members of two young children that were shot on July 4 in Chicago wait outside Comer Children's Hospital. In the first six months of the year, 15 children younger than 10 were shot, none fatally. That's seven more than in the first half of 2015

Demonstrators and police are pictured during a protest of Laquan McDonald's shooting. The city is making major changes to the department and various oversight bodies after the uproar over the 2014 shooting in which McDonald was shot 16 times by a white officer

In New York City, which has a police department of 34,450, 15 per cent are detectives.

In Los Angeles, which has a police department of 9,800 sworn officers, 15 per cent 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.

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.

HOMICIDES AND SHOOTINGS ON THE RISE IN CHICAGO There were 441 homicides in the city between the start of the year and August 21, a nearly 50 per cent increase over the same period last year, police said. That's also more than 80 per cent higher than at the same point in 2014, when the city ended the year with just over 400 homicides — the least in a half-century. Other cities, such as Los Angeles and Memphis, Tennessee, also have seen homicides rise, according to a midyear survey by the Major Cities Chiefs Association. But experts said it is not enough to suggest a trend, noting numbers are down elsewhere, such as Oakland, California, and Miami. Much of the increase in Chicago homicides is related to more shootings, which have been climbing since 2013 but have spiked this year to 2,228 as of August 21. That's 48 per cent more than in the same time frame last year, and easily surpasses the total recorded in all of 2014, when there were 2,084. Advertisement

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 per cent 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 are frustrated that police have not found even a suspect.

The fatal shooting of NBA star Dwyane Wade's cousin is the latest in the sharp uptick in gun violence in Chicago.

Nykea Aldridge was killed on Friday afternoon while pushing her baby in a stroller near a school.

NBA star Dwyane Wade's cousin, Nykea Aldridge (pictured), was killed on Friday afternoon in Chicago while pushing her baby in a stroller near a school

The Chicago Bulls player wrote on Twitter: 'My cousin was killed today in Chicago. Another act of senseless gun violence. Four kids lost their mom for NO REASON. Unreal'

Chicago Police spokesman Anthony Guglielmi said on Saturday two 'people of interest' are being interrogated by detectives.

He said police also are investigating whether the encounter involved a driver for a ride-share company.

Police said two males walked up and began shooting at a third man but hit the 32-year-old mother of four in the head and arm.

Guglielmi said she was not the intended target.

She recently relocated to the neighborhood on the city's South Side, about one-and-a-half miles southwest of the University of Chicago, according to her family.

She is among the many innocent people who have been hit by stray gunfire, including a growing number of young children.

In the first six months of the year, 15 children younger than 10 were shot, none fatally. That's seven more than in the first half of 2015.

The victims included a six-year-old girl who was drawing with sidewalk chalk when she was shot in the back with a bullet intended for rival gang members.

A bullet pierced the cheek of a four-year-old boy as he walked down a sidewalk, holding his mother's hand.