A young boxer in the Bronx, New York, was shot dead outside a bodega at 3:30 a.m. on a Saturday last August. Weeks later, a 59-year-old woman was beaten to death on a Saturday night on the side of a highway in Queens. On the last Sunday in September, violence exploded as five men were killed in a spate of shootings and stabbings between midnight and 6 a.m.

Seven homicides in New York City. None connected in any way but this: They happened during the summer months, when the temperatures rise, people hit the streets, and New York becomes a more lethal place.

There were more homicides in September than in any other month last year: 52. Next highest was August, with 51.

The prime time for murder is clear: summertime. And the breakdown of deadly brutality can get even more specific. September Saturdays around 10 p.m. were the most likely moments for a murder.

The summer spike in killings is just one of several findings unearthed in an analysis by The New York Times of multiyear homicide trends. The information - detailing homicides during the years 2003 to 2008 - was compiled mainly from open-records requests with the New York Police Department, and a database of details on homicides in the city during those years is available online at nytimes. com/nyregion.

Of course, the most important trend involving murder in New York has been the enormous decline in killings over the last 15 years.

Still, hundreds of people are killed every year in the city, and The Times’s findings provide insights about who is killed in New York, as well as who does the killing, where murders occur and why.

Women, for instance, are less likely to be either victims or killers. Those who were killed - at least 73 women were in 2008 - were almost always murdered by someone they knew - boyfriends, husbands or relatives. From 2003 to 2008, the number of women killed each year by strangers was in the single digits - excluding cases in which the police do not know if the killer knew the victim.

More often than not, the weapon of choice is a firearm. Each year the percentage of people killed by firearms hovers around 60 percent. Of all the trends to emerge, the time for killing was among the most enduring.

In New York, the trend goes back well before the years covered in the database - at least as far as 1981, according to an analysis of reports by the city medical examiner’s office done by Steven F. Messner, a criminology professor at the State University of New York at Albany. And he believes it stretches back much further than that.

Nationally, in the early 1980s, scientists at the Centers for Disease Control and Prevention analyzed a decade’s worth of data across the nation, and found that homicides swell between July and September.

A prime reason murder peaks during this time has to do with the routines of people’s lives, according to Professor Messner. Summer is when people get together. More specifically, casual drinkers and drug users are more likely to go to bars or parties on weekends and evenings.

And the trend occurs in other cities, according to criminologists.

Failing to understand the basic connection between time of year and homicide rates can lead law enforcement agencies to faulty conclusions about what is happening in the streets - and it can affect their strategies.

In New York, in the early 1990s, police managers altered the working hours for some detectives, including those tracking narcotics cases and those seeking to arrest criminals wanted on open warrants. It seemed to the top officials at the time that too many officers were ending their shifts at dusk and taking weekends off.

Jack Maple, a former police deputy commissioner who wrote a book, “The Crime Fighter,” described the shortfall this way: “Unfortunately, the bad guys work around the clock.”

And in the summer months, the bad guys tend to be deadliest.

By ANDREW W. LEHREN and AL BAKER