Closing time was drawing near when the call came crackling over the police radio: Person knocked out during a fight, 20th and Market streets.

Denver police Lt. Marion Penn spun the wheel of his squad car and headed into the volatile parade of drunken revelry that defines Lower Downtown in the wee hours of a Saturday.

Some people are just trying to make it home safely — and some people won’t make it home at all.

Drunken women teetered on high heels. One squealed as her boyfriend hoisted her onto his shoulders. They laughed.

Splayed on the asphalt by the couple’s feet, the assault victim lay motionless, blood pooling around his head. Two guys had spotted him as he left a bar, jumped out of their truck, slugged him and drove away. Paramedics braced his neck and loaded him onto an ambulance while officers radioed to be on the lookout for the pickup.

“This is probably not the only assault we’ll see tonight,” an officer said.

It wasn’t.

Closing time marks a dark divide on the streets of LoDo, where the night’s festivities wind down and tempers, fights and arrests amp up. While the rest of the city sleeps, the 25-block radius comes alive with its own chaotic rhythm as thousands of people pour into the streets, and the paramedics, police and bar bouncers struggle to clear the area and keep the peace.

A person is more likely to be a crime victim between 1 and 3 a.m. in LoDo than in any other part of the city at that time, an analysis of police data shows.

On just one morning this month, a 19-year-old Buckley airman was shot to death at 15th and Market streets during closing time, just as a group of gang members attacked two people, a man shot himself in the leg and another man fired a gun into the air.

“I know there are shootings and stuff, but you don’t really think about it while you’re out,” said Janna Moreau, 23, who often comes to LoDo and keeps her boyfriend nearby. “There’s fights all the time. It’s drunk guys trying to prove themselves, and they don’t bother you. I usually just try to walk with the crowd.”

The Denver Post rode with police and spent several early mornings on the streets of LoDo to get a sense of closing time. Dance music throbs from the doors of nightclubs as the hours wear on. What starts as an orderly night on the town often devolves into a rowdy scene.

Despite the efforts of police officers and bar owners who spend tens of thousands of dollars on security, the violence persists.

LoDo’s boundaries are defined differently by different people. But all agree the stakes of keeping the neighborhood safe are high. LoDo — which the police department defines as 20th Street to Larimer Street and Speer Boulevard to Wewatta Street — generated $8.1 million in sales tax revenue last year, according to Denver’s finance department. More than 82 percent of that was “night-life tax,” generated by bars, restaurants and hotels.

There were 682 violent crimes — assaults, robberies, rapes, shots fired — between July 1, 2012, and June 30 in the police precincts encompassing LoDo, and 330 occurred in the first six months of this year, according to an analysis of Denver police data by the Colfax Coalition, a group of neighborhood organizations that earlier this year urged city officials to address the problems at closing time. There were 387 violent incidents during the first six months of last year.

Eighty violent crimes in those precincts were reported this past June alone.

Many of the incidents were reported at intersections, suggesting that most of the problems unfold on the street. The corner of 15th and Market ranked as a top offender, with 13 violent crimes reported there between July 1, 2012, and June 30, the coalition found.

Closing time — mandated by state liquor laws as 2 a.m. — concentrates the dangerous cocktail of alcohol, testosterone and too many people who aren’t ready to go home. Dozens of bars send thousands of patrons into the night at once, leading to loud noise, public urination, countless fights, stabbings and worse.

The recent troubles have reignited a discussion about how to handle the “outcrowds.” Nightclubs have debated everything from staggering their closing times and earlier “last calls” to erecting lamps so bright they would simulate daylight and send partygoers scattering.

“Each time there is an incident in the neighborhood, we come together and we organize and we try to find a solution,” said Denver Councilwoman Judy Montero, whose district includes LoDo. “Some good things have come out of it. But the thing is, there’s not just one solution. That’s what takes more time and more discussion and attention to detail. It takes constant work.”

Finding a fix will mean taking a wholesale look at everything from the issuance of liquor licenses to the positioning of street lamps and the presence of late-night food vendors.

Despite the recent violence, some bar patrons and neighbors say the scene has improved in recent years.

“This summer is significantly better in terms of crowds and that unsafe feeling you get at let-out,” Lower Downtown Neighborhood Association president Josh Davies said.

The improvements are in part because of the group’s efforts, including the “good-neighbor agreements” it has implored bar owners to sign. The organization was among those that raised money for extra officers and a “scout car,” which District 6 police Cmdr. Tony Lopez described as a Denver sheriff’s van that can roam LoDo, taking publicly inebriated people to detox or jail so that police officers can stay on the street.

But for the officers who work the overnight shift or moonlight as uniformed security guards at LoDo establishments, the outcrowds remain a frustrating problem. Longtime District 6 officers grow weary of battling belligerent drunks. On a recent Sunday morning, they used pepper spray to defuse a melee near 20th and Market. In a separate brawl five blocks away, a private security guard unleashed pepper spray to end a fight in a parking lot. In its aftermath, a woman in a short, tight dress sat in the back seat of a squad car, mascara streaking from her eyes.

“If you let (the crowd) handle itself, it won’t work. There will be a fight, and then fight after fight after fight after fight,” said Penn, who once patrolled the downtown streets and now supervises the overnight weekend shift.

Groups of four or five on-duty officers have started assembling at the notorious trouble spots just before closing time, when the 911 center gets a surge of calls; records show calls for service can quadruple between midnight and 3 a.m. on summer Sundays. They move pedestrians down the road, break up fights and keep the cabs from idling. They’re also there to curb the occurrence of “parking lot pimping,” when men who have never entered the bars cruise the street. They’re looking for a hookup or for trouble, one officer explained, and they typically have no difficulty finding either.

Police made at least 12 arrests between July 12 and 15, the weekend the airman, Shaquille Hargrove, was shot. The charges: firing or discharging a gun, first-degree assault, public consumption of alcohol, drunken driving, disturbing the peace and trespass. Another man was picked up on an outstanding warrant, while another had hypodermic needles.

“It’s one of those issues that, unless there’s a breakthrough with some new, innovative strategy, we’re just going to continue to monitor it,” Mayor Michael Hancock said Friday, adding that bar owners, neighborhood groups and police have an ongoing conversation about how best to handle safety in what he described as a “very vibrant area.”

“This is a safe area. The police department has done a great job to redistribute resources during peak times,” he said. “Major cities that have entertainment districts are going to have times when there are skirmishes. You’re going to have people who make bad decisions. It’s a byproduct of a very successful area.”

Lopez said that for most people, LoDo remains a comfortable environment and that the deadly shooting happened during a “perfect storm.”

The crowds, he said, are a sign that people still feel safe.

“One bad night gives us a black eye, we recognize that,” he said. “This weekend, it will be busy again.”

This summer isn’t close to being LoDo’s worst. In 2009, for example, there were at least 26 incidents police described as racially motivated assaults and robberies downtown, including in LoDo. Detectives arrested scores of men and boys, most of whom said they were connected to gangs. And in 2008, a closing-time gunfight in a parking lot at 18th and Market, in which officers killed one man and wounded another who fired a shotgun at them, highlighted crowd-control problems in the strip of numerous nightclubs.

Kendall Wilson, 24, often parties near 15th and Market, and the shooting of Hargrove won’t deter her from going back, she said as she and friends chatted at the ViewHouse at 20th and Market on Thursday. Fights are known to crop up outside that bar as thousands of people leave.

“I’m not scared of what’s going on. It’s always fun,” she said. “But a lot of my friends are very hesitant.”

No other neighborhood in Denver sees the same kinds of issues in the same volume as LoDo, including the busy South Broadway district, where police have also recently focused their attention during closing time.

After the killing, police officers returned to their practice of using their squad cars to shut down the busiest LoDo streets about 1:30 a.m. Their presence helps clear the streets, but they can’t prevent it all.

The problem is larger than the police, Penn said.

“You will not stop LoDo. It won’t happen,” he said. “A lot of the officers out here, they’ve been here a long time. The only thing I tell these guys with outcrowds in LoDo is, be there. Presence and consistency. That’s what helps us.”

The calls continued to come in on a recent night. At 20th and Market, a female 911 caller screamed “Stop chasing me!” before she hung up. At 16th and Market, someone was knocked out.

“What you have is, over the course of the evening, a group of people that gets larger and larger and consumes more and more alcohol. At exactly 1:45 a.m., they’re all flushed out directly into the system,” said Scott Bookman, chief paramedic for Denver Health Medical Center, which stations ambulances on LoDo’s perimeter on weekend nights.

The combination of alcohol and crowds, he said, is “fraught with peril.”

“You’ve got people who are literally vomiting and passed out,” he said. “You’ve got people who are literally falling because they’re too intoxicated to walk properly. And then, of course, you have the violence.”

The 911 calls surge between midnight and 3 a.m., he said.

“Everybody’s got a cellphone, and everybody’s calling 911 when something happens. There’s a lot of misinformation, a lot of people calling 911 for the same person,” Bookman said.

The assault call at 20th and Market, for example, also came in as a stabbing. Penn radioed to dispatchers that the calls were one and the same.

“Sometimes you walk into the crowd, and you run into someone who hasn’t had a chance to call 911,” said Bookman, whose former position as a Saturday night supervisor often brought him into the heart of LoDo. “I found it to be a great challenge.”

In its study, the Colfax Coalition found that 41 percent of downtown violence happens overnight Thursday, Friday and Saturday — specifically, between 11 p.m. and 4 a.m.

Among the group’s other findings:

• While crime elsewhere in the city was down in 2012, aggravated assaults downtown were up 14 percent and robberies 31 percent.

• Violent crime rates on a Saturday night are more than four times that of a “typical” Sunday, Monday, Tuesday or Wednesday night.

• Fifty-two percent of violent crimes on a Saturday night happened between 1 and 3 a.m. — the bookends of closing time.

Heat maps created by the group showed a strong correlation between crimes against persons and the location of liquor-licensed establishments, specifically at closing time.

Chuck Sampson, a coalition board member who compiled the report, said part of the problem is a city policy that allows an existing liquor license to be transferred to a new owner, circumventing a public “needs and desires” hearing that new applicants would face. And now LoDo is saturated.

“It’s going to take everyone working together to figure out what’s the solution,” Sampson said. “Unless we do something, it’s not going to get any better.”

Looking at figures such as officers’ salaries, jail and overtime costs, the group estimated that bar-closing efforts cost the city $913,000 a year.

Montero, the councilwoman, said the challenge is in finding a balance between promoting a vibrant entertainment district and keeping the neighbors comfortable and safe. Residents awaken to beer bottles, remnants of half-eaten burritos, pizza crusts and the stench of urine.

“Usually when you’ve got a pool of vomit in your front door, you don’t need a lot of it for it to be a problem,” said Davies, who lives at 14th and Wewatta. “It’s not terrible, but it’s one of those things that adds up over time.”

It’s a struggle, but incidents of violence are rarer than the media make them seem, said George Mannion, a managing partner of LoDo’s Bar & Grill, near 19th and Market, an area that is home to four venues that hold more than 1,000 people. It takes a lot to keep the bar safe. Mannion said he pays three or four off-duty Denver officers $45 an hour to keep the peace as well as 20 doormen who try to keep drunks from driving.

“It’s part of the challenge of doing business in our market,” Mannion said. “We’re in the business of handling large crowds. It’s part of our job.”

It’s not always easy. The Colfax Coalition studied 2012 violent-crime reports that show the stretch of Market Street is among the top locations for aggravated assaults. Nine assaults and a purse snatching were reported at the LoDo’s Bar & Grill address last year, the study said.

Jeremy Garcia, a server and former bouncer at The Tavern, just across Market Street, described a nightly struggle to keep people from loitering or rushing to back bathrooms when the lights go on and it’s closing time.

“People are still in the mood, people still want to party,” he said. “I tell people to chug their beers on the way out.” Bouncers fan out, pushing guests toward the doors.

Outside, the taxis and pedicabs lie in wait. They seem eager to offer a ride, raising their prices as the night wears on. But some have their misgivings.

“It introduced me to a sector of society that I knew existed but never experienced,” said one pedicab driver, Phil Ross. “There’s a lot of people who, for some reason, have lots of expendable cash and not a lot of responsibility. They feel like they can just kind of be crazy.”

Even the most seasoned LoDo partyers feel the challenges of closing time.

Kelc Martini, 23, complained of the difficulty in getting a taxi. She and fellow students at the Denver School of Nursing on 19th Street come to LoDo bars because the area is close, but they’re aware of the risks.

“It is chaos. The cops are always down here. People are literally getting laid down in the street. But it’s a good time,” said another nursing student, Jack Lariviere, 27, who was enjoying drinks with Martini and friends at Maloney’s Tavern on a much quieter Tuesday night.

They joked about people urinating in alleys and how they carry pepper spray. One woman said she carries a gun. They recalled the Saturday in April when they were at Summit Music Hall at 19th and Blake when an assault drew hoards of police and sent a man to the hospital in critical condition.

“It’s fine!” one woman said. “It’s seriously not that bad! Where would you prefer to be?”

Sadie Gurman: 303-954-1661, sgurman@denverpost.com or twitter.com/sgurman